diff --git "a/testbed/django__django/tests/model_forms/tests.py" "b/testbed/django__django/tests/model_forms/tests.py"
new file mode 100644--- /dev/null
+++ "b/testbed/django__django/tests/model_forms/tests.py"
@@ -0,0 +1,3688 @@
+import datetime
+import os
+from decimal import Decimal
+from unittest import mock, skipUnless
+
+from django import forms
+from django.core.exceptions import (
+    NON_FIELD_ERRORS,
+    FieldError,
+    ImproperlyConfigured,
+    ValidationError,
+)
+from django.core.files.uploadedfile import SimpleUploadedFile
+from django.db import connection, models
+from django.db.models.query import EmptyQuerySet
+from django.forms.models import (
+    ModelFormMetaclass,
+    construct_instance,
+    fields_for_model,
+    model_to_dict,
+    modelform_factory,
+)
+from django.template import Context, Template
+from django.test import SimpleTestCase, TestCase, ignore_warnings, skipUnlessDBFeature
+from django.test.utils import isolate_apps
+from django.utils.deprecation import RemovedInDjango60Warning
+
+from .models import (
+    Article,
+    ArticleStatus,
+    Author,
+    Author1,
+    Award,
+    BetterWriter,
+    BigInt,
+    Book,
+    Category,
+    Character,
+    Colour,
+    ColourfulItem,
+    CustomErrorMessage,
+    CustomFF,
+    CustomFieldForExclusionModel,
+    DateTimePost,
+    DerivedBook,
+    DerivedPost,
+    Dice,
+    Document,
+    ExplicitPK,
+    FilePathModel,
+    FlexibleDatePost,
+    Homepage,
+    ImprovedArticle,
+    ImprovedArticleWithParentLink,
+    Inventory,
+    NullableUniqueCharFieldModel,
+    Number,
+    Person,
+    Photo,
+    Post,
+    Price,
+    Product,
+    Publication,
+    PublicationDefaults,
+    StrictAssignmentAll,
+    StrictAssignmentFieldSpecific,
+    Student,
+    StumpJoke,
+    TextFile,
+    Triple,
+    Writer,
+    WriterProfile,
+    test_images,
+)
+
+if test_images:
+    from .models import ImageFile, NoExtensionImageFile, OptionalImageFile
+
+    class ImageFileForm(forms.ModelForm):
+        class Meta:
+            model = ImageFile
+            fields = "__all__"
+
+    class OptionalImageFileForm(forms.ModelForm):
+        class Meta:
+            model = OptionalImageFile
+            fields = "__all__"
+
+    class NoExtensionImageFileForm(forms.ModelForm):
+        class Meta:
+            model = NoExtensionImageFile
+            fields = "__all__"
+
+
+class ProductForm(forms.ModelForm):
+    class Meta:
+        model = Product
+        fields = "__all__"
+
+
+class PriceForm(forms.ModelForm):
+    class Meta:
+        model = Price
+        fields = "__all__"
+
+
+class BookForm(forms.ModelForm):
+    class Meta:
+        model = Book
+        fields = "__all__"
+
+
+class DerivedBookForm(forms.ModelForm):
+    class Meta:
+        model = DerivedBook
+        fields = "__all__"
+
+
+class ExplicitPKForm(forms.ModelForm):
+    class Meta:
+        model = ExplicitPK
+        fields = (
+            "key",
+            "desc",
+        )
+
+
+class PostForm(forms.ModelForm):
+    class Meta:
+        model = Post
+        fields = "__all__"
+
+
+class DerivedPostForm(forms.ModelForm):
+    class Meta:
+        model = DerivedPost
+        fields = "__all__"
+
+
+class CustomWriterForm(forms.ModelForm):
+    name = forms.CharField(required=False)
+
+    class Meta:
+        model = Writer
+        fields = "__all__"
+
+
+class BaseCategoryForm(forms.ModelForm):
+    class Meta:
+        model = Category
+        fields = "__all__"
+
+
+class ArticleForm(forms.ModelForm):
+    class Meta:
+        model = Article
+        fields = "__all__"
+
+
+class RoykoForm(forms.ModelForm):
+    class Meta:
+        model = Writer
+        fields = "__all__"
+
+
+class ArticleStatusForm(forms.ModelForm):
+    class Meta:
+        model = ArticleStatus
+        fields = "__all__"
+
+
+class InventoryForm(forms.ModelForm):
+    class Meta:
+        model = Inventory
+        fields = "__all__"
+
+
+class SelectInventoryForm(forms.Form):
+    items = forms.ModelMultipleChoiceField(
+        Inventory.objects.all(), to_field_name="barcode"
+    )
+
+
+class CustomFieldForExclusionForm(forms.ModelForm):
+    class Meta:
+        model = CustomFieldForExclusionModel
+        fields = ["name", "markup"]
+
+
+class TextFileForm(forms.ModelForm):
+    class Meta:
+        model = TextFile
+        fields = "__all__"
+
+
+class BigIntForm(forms.ModelForm):
+    class Meta:
+        model = BigInt
+        fields = "__all__"
+
+
+class ModelFormWithMedia(forms.ModelForm):
+    class Media:
+        js = ("/some/form/javascript",)
+        css = {"all": ("/some/form/css",)}
+
+    class Meta:
+        model = TextFile
+        fields = "__all__"
+
+
+class CustomErrorMessageForm(forms.ModelForm):
+    name1 = forms.CharField(error_messages={"invalid": "Form custom error message."})
+
+    class Meta:
+        fields = "__all__"
+        model = CustomErrorMessage
+
+
+class ModelFormBaseTest(TestCase):
+    def test_base_form(self):
+        self.assertEqual(list(BaseCategoryForm.base_fields), ["name", "slug", "url"])
+
+    def test_no_model_class(self):
+        class NoModelModelForm(forms.ModelForm):
+            pass
+
+        with self.assertRaisesMessage(
+            ValueError, "ModelForm has no model class specified."
+        ):
+            NoModelModelForm()
+
+    def test_empty_fields_to_fields_for_model(self):
+        """
+        An argument of fields=() to fields_for_model should return an empty dictionary
+        """
+        field_dict = fields_for_model(Person, fields=())
+        self.assertEqual(len(field_dict), 0)
+
+    def test_fields_for_model_form_fields(self):
+        form_declared_fields = CustomWriterForm.declared_fields
+        field_dict = fields_for_model(
+            Writer,
+            fields=["name"],
+            form_declared_fields=form_declared_fields,
+        )
+        self.assertIs(field_dict["name"], form_declared_fields["name"])
+
+    def test_empty_fields_on_modelform(self):
+        """
+        No fields on a ModelForm should actually result in no fields.
+        """
+
+        class EmptyPersonForm(forms.ModelForm):
+            class Meta:
+                model = Person
+                fields = ()
+
+        form = EmptyPersonForm()
+        self.assertEqual(len(form.fields), 0)
+
+    def test_empty_fields_to_construct_instance(self):
+        """
+        No fields should be set on a model instance if construct_instance
+        receives fields=().
+        """
+        form = modelform_factory(Person, fields="__all__")({"name": "John Doe"})
+        self.assertTrue(form.is_valid())
+        instance = construct_instance(form, Person(), fields=())
+        self.assertEqual(instance.name, "")
+
+    def test_blank_with_null_foreign_key_field(self):
+        """
+        #13776 -- ModelForm's with models having a FK set to null=False and
+        required=False should be valid.
+        """
+
+        class FormForTestingIsValid(forms.ModelForm):
+            class Meta:
+                model = Student
+                fields = "__all__"
+
+            def __init__(self, *args, **kwargs):
+                super().__init__(*args, **kwargs)
+                self.fields["character"].required = False
+
+        char = Character.objects.create(
+            username="user", last_action=datetime.datetime.today()
+        )
+        data = {"study": "Engineering"}
+        data2 = {"study": "Engineering", "character": char.pk}
+
+        # form is valid because required=False for field 'character'
+        f1 = FormForTestingIsValid(data)
+        self.assertTrue(f1.is_valid())
+
+        f2 = FormForTestingIsValid(data2)
+        self.assertTrue(f2.is_valid())
+        obj = f2.save()
+        self.assertEqual(obj.character, char)
+
+    def test_blank_false_with_null_true_foreign_key_field(self):
+        """
+        A ModelForm with a model having ForeignKey(blank=False, null=True)
+        and the form field set to required=False should allow the field to be
+        unset.
+        """
+
+        class AwardForm(forms.ModelForm):
+            class Meta:
+                model = Award
+                fields = "__all__"
+
+            def __init__(self, *args, **kwargs):
+                super().__init__(*args, **kwargs)
+                self.fields["character"].required = False
+
+        character = Character.objects.create(
+            username="user", last_action=datetime.datetime.today()
+        )
+        award = Award.objects.create(name="Best sprinter", character=character)
+        data = {"name": "Best tester", "character": ""}  # remove character
+        form = AwardForm(data=data, instance=award)
+        self.assertTrue(form.is_valid())
+        award = form.save()
+        self.assertIsNone(award.character)
+
+    def test_blank_foreign_key_with_radio(self):
+        class BookForm(forms.ModelForm):
+            class Meta:
+                model = Book
+                fields = ["author"]
+                widgets = {"author": forms.RadioSelect()}
+
+        writer = Writer.objects.create(name="Joe Doe")
+        form = BookForm()
+        self.assertEqual(
+            list(form.fields["author"].choices),
+            [
+                ("", "---------"),
+                (writer.pk, "Joe Doe"),
+            ],
+        )
+
+    def test_non_blank_foreign_key_with_radio(self):
+        class AwardForm(forms.ModelForm):
+            class Meta:
+                model = Award
+                fields = ["character"]
+                widgets = {"character": forms.RadioSelect()}
+
+        character = Character.objects.create(
+            username="user",
+            last_action=datetime.datetime.today(),
+        )
+        form = AwardForm()
+        self.assertEqual(
+            list(form.fields["character"].choices),
+            [(character.pk, "user")],
+        )
+
+    def test_save_blank_false_with_required_false(self):
+        """
+        A ModelForm with a model with a field set to blank=False and the form
+        field set to required=False should allow the field to be unset.
+        """
+        obj = Writer.objects.create(name="test")
+        form = CustomWriterForm(data={"name": ""}, instance=obj)
+        self.assertTrue(form.is_valid())
+        obj = form.save()
+        self.assertEqual(obj.name, "")
+
+    @ignore_warnings(category=RemovedInDjango60Warning)
+    def test_save_blank_null_unique_charfield_saves_null(self):
+        form_class = modelform_factory(
+            model=NullableUniqueCharFieldModel, fields="__all__"
+        )
+        empty_value = (
+            "" if connection.features.interprets_empty_strings_as_nulls else None
+        )
+        data = {
+            "codename": "",
+            "email": "",
+            "slug": "",
+            "url": "",
+        }
+        form = form_class(data=data)
+        self.assertTrue(form.is_valid())
+        form.save()
+        self.assertEqual(form.instance.codename, empty_value)
+        self.assertEqual(form.instance.email, empty_value)
+        self.assertEqual(form.instance.slug, empty_value)
+        self.assertEqual(form.instance.url, empty_value)
+
+        # Save a second form to verify there isn't a unique constraint violation.
+        form = form_class(data=data)
+        self.assertTrue(form.is_valid())
+        form.save()
+        self.assertEqual(form.instance.codename, empty_value)
+        self.assertEqual(form.instance.email, empty_value)
+        self.assertEqual(form.instance.slug, empty_value)
+        self.assertEqual(form.instance.url, empty_value)
+
+    def test_missing_fields_attribute(self):
+        message = (
+            "Creating a ModelForm without either the 'fields' attribute "
+            "or the 'exclude' attribute is prohibited; form "
+            "MissingFieldsForm needs updating."
+        )
+        with self.assertRaisesMessage(ImproperlyConfigured, message):
+
+            class MissingFieldsForm(forms.ModelForm):
+                class Meta:
+                    model = Category
+
+    def test_extra_fields(self):
+        class ExtraFields(BaseCategoryForm):
+            some_extra_field = forms.BooleanField()
+
+        self.assertEqual(
+            list(ExtraFields.base_fields), ["name", "slug", "url", "some_extra_field"]
+        )
+
+    def test_extra_field_model_form(self):
+        with self.assertRaisesMessage(FieldError, "no-field"):
+
+            class ExtraPersonForm(forms.ModelForm):
+                """ModelForm with an extra field"""
+
+                age = forms.IntegerField()
+
+                class Meta:
+                    model = Person
+                    fields = ("name", "no-field")
+
+    def test_extra_declared_field_model_form(self):
+        class ExtraPersonForm(forms.ModelForm):
+            """ModelForm with an extra field"""
+
+            age = forms.IntegerField()
+
+            class Meta:
+                model = Person
+                fields = ("name", "age")
+
+    def test_extra_field_modelform_factory(self):
+        with self.assertRaisesMessage(
+            FieldError, "Unknown field(s) (no-field) specified for Person"
+        ):
+            modelform_factory(Person, fields=["no-field", "name"])
+
+    def test_replace_field(self):
+        class ReplaceField(forms.ModelForm):
+            url = forms.BooleanField()
+
+            class Meta:
+                model = Category
+                fields = "__all__"
+
+        self.assertIsInstance(
+            ReplaceField.base_fields["url"], forms.fields.BooleanField
+        )
+
+    def test_replace_field_variant_2(self):
+        # Should have the same result as before,
+        # but 'fields' attribute specified differently
+        class ReplaceField(forms.ModelForm):
+            url = forms.BooleanField()
+
+            class Meta:
+                model = Category
+                fields = ["url"]
+
+        self.assertIsInstance(
+            ReplaceField.base_fields["url"], forms.fields.BooleanField
+        )
+
+    def test_replace_field_variant_3(self):
+        # Should have the same result as before,
+        # but 'fields' attribute specified differently
+        class ReplaceField(forms.ModelForm):
+            url = forms.BooleanField()
+
+            class Meta:
+                model = Category
+                fields = []  # url will still appear, since it is explicit above
+
+        self.assertIsInstance(
+            ReplaceField.base_fields["url"], forms.fields.BooleanField
+        )
+
+    def test_override_field(self):
+        class WriterForm(forms.ModelForm):
+            book = forms.CharField(required=False)
+
+            class Meta:
+                model = Writer
+                fields = "__all__"
+
+        wf = WriterForm({"name": "Richard Lockridge"})
+        self.assertTrue(wf.is_valid())
+
+    def test_limit_nonexistent_field(self):
+        expected_msg = "Unknown field(s) (nonexistent) specified for Category"
+        with self.assertRaisesMessage(FieldError, expected_msg):
+
+            class InvalidCategoryForm(forms.ModelForm):
+                class Meta:
+                    model = Category
+                    fields = ["nonexistent"]
+
+    def test_limit_fields_with_string(self):
+        msg = (
+            "CategoryForm.Meta.fields cannot be a string. Did you mean to type: "
+            "('url',)?"
+        )
+        with self.assertRaisesMessage(TypeError, msg):
+
+            class CategoryForm(forms.ModelForm):
+                class Meta:
+                    model = Category
+                    fields = "url"  # note the missing comma
+
+    def test_exclude_fields(self):
+        class ExcludeFields(forms.ModelForm):
+            class Meta:
+                model = Category
+                exclude = ["url"]
+
+        self.assertEqual(list(ExcludeFields.base_fields), ["name", "slug"])
+
+    def test_exclude_nonexistent_field(self):
+        class ExcludeFields(forms.ModelForm):
+            class Meta:
+                model = Category
+                exclude = ["nonexistent"]
+
+        self.assertEqual(list(ExcludeFields.base_fields), ["name", "slug", "url"])
+
+    def test_exclude_fields_with_string(self):
+        msg = (
+            "CategoryForm.Meta.exclude cannot be a string. Did you mean to type: "
+            "('url',)?"
+        )
+        with self.assertRaisesMessage(TypeError, msg):
+
+            class CategoryForm(forms.ModelForm):
+                class Meta:
+                    model = Category
+                    exclude = "url"  # note the missing comma
+
+    def test_exclude_and_validation(self):
+        # This Price instance generated by this form is not valid because the quantity
+        # field is required, but the form is valid because the field is excluded from
+        # the form. This is for backwards compatibility.
+        class PriceFormWithoutQuantity(forms.ModelForm):
+            class Meta:
+                model = Price
+                exclude = ("quantity",)
+
+        form = PriceFormWithoutQuantity({"price": "6.00"})
+        self.assertTrue(form.is_valid())
+        price = form.save(commit=False)
+        msg = "{'quantity': ['This field cannot be null.']}"
+        with self.assertRaisesMessage(ValidationError, msg):
+            price.full_clean()
+
+        # The form should not validate fields that it doesn't contain even if they are
+        # specified using 'fields', not 'exclude'.
+        class PriceFormWithoutQuantity(forms.ModelForm):
+            class Meta:
+                model = Price
+                fields = ("price",)
+
+        form = PriceFormWithoutQuantity({"price": "6.00"})
+        self.assertTrue(form.is_valid())
+
+        # The form should still have an instance of a model that is not complete and
+        # not saved into a DB yet.
+        self.assertEqual(form.instance.price, Decimal("6.00"))
+        self.assertIsNone(form.instance.quantity)
+        self.assertIsNone(form.instance.pk)
+
+    def test_confused_form(self):
+        class ConfusedForm(forms.ModelForm):
+            """Using 'fields' *and* 'exclude'. Not sure why you'd want to do
+            this, but uh, "be liberal in what you accept" and all.
+            """
+
+            class Meta:
+                model = Category
+                fields = ["name", "url"]
+                exclude = ["url"]
+
+        self.assertEqual(list(ConfusedForm.base_fields), ["name"])
+
+    def test_mixmodel_form(self):
+        class MixModelForm(BaseCategoryForm):
+            """Don't allow more than one 'model' definition in the
+            inheritance hierarchy.  Technically, it would generate a valid
+            form, but the fact that the resulting save method won't deal with
+            multiple objects is likely to trip up people not familiar with the
+            mechanics.
+            """
+
+            class Meta:
+                model = Article
+                fields = "__all__"
+
+            # MixModelForm is now an Article-related thing, because MixModelForm.Meta
+            # overrides BaseCategoryForm.Meta.
+
+        self.assertEqual(
+            list(MixModelForm.base_fields),
+            [
+                "headline",
+                "slug",
+                "pub_date",
+                "writer",
+                "article",
+                "categories",
+                "status",
+            ],
+        )
+
+    def test_article_form(self):
+        self.assertEqual(
+            list(ArticleForm.base_fields),
+            [
+                "headline",
+                "slug",
+                "pub_date",
+                "writer",
+                "article",
+                "categories",
+                "status",
+            ],
+        )
+
+    def test_bad_form(self):
+        # First class with a Meta class wins...
+        class BadForm(ArticleForm, BaseCategoryForm):
+            pass
+
+        self.assertEqual(
+            list(BadForm.base_fields),
+            [
+                "headline",
+                "slug",
+                "pub_date",
+                "writer",
+                "article",
+                "categories",
+                "status",
+            ],
+        )
+
+    def test_invalid_meta_model(self):
+        class InvalidModelForm(forms.ModelForm):
+            class Meta:
+                pass  # no model
+
+        # Can't create new form
+        msg = "ModelForm has no model class specified."
+        with self.assertRaisesMessage(ValueError, msg):
+            InvalidModelForm()
+
+        # Even if you provide a model instance
+        with self.assertRaisesMessage(ValueError, msg):
+            InvalidModelForm(instance=Category)
+
+    def test_subcategory_form(self):
+        class SubCategoryForm(BaseCategoryForm):
+            """Subclassing without specifying a Meta on the class will use
+            the parent's Meta (or the first parent in the MRO if there are
+            multiple parent classes).
+            """
+
+            pass
+
+        self.assertEqual(list(SubCategoryForm.base_fields), ["name", "slug", "url"])
+
+    def test_subclassmeta_form(self):
+        class SomeCategoryForm(forms.ModelForm):
+            checkbox = forms.BooleanField()
+
+            class Meta:
+                model = Category
+                fields = "__all__"
+
+        class SubclassMeta(SomeCategoryForm):
+            """We can also subclass the Meta inner class to change the fields
+            list.
+            """
+
+            class Meta(SomeCategoryForm.Meta):
+                exclude = ["url"]
+
+        self.assertHTMLEqual(
+            str(SubclassMeta()),
+            '<div><label for="id_name">Name:</label>'
+            '<input type="text" name="name" maxlength="20" required id="id_name">'
+            '</div><div><label for="id_slug">Slug:</label><input type="text" '
+            'name="slug" maxlength="20" required id="id_slug"></div><div>'
+            '<label for="id_checkbox">Checkbox:</label>'
+            '<input type="checkbox" name="checkbox" required id="id_checkbox"></div>',
+        )
+
+    def test_orderfields_form(self):
+        class OrderFields(forms.ModelForm):
+            class Meta:
+                model = Category
+                fields = ["url", "name"]
+
+        self.assertEqual(list(OrderFields.base_fields), ["url", "name"])
+        self.assertHTMLEqual(
+            str(OrderFields()),
+            '<div><label for="id_url">The URL:</label>'
+            '<input type="text" name="url" maxlength="40" required id="id_url">'
+            '</div><div><label for="id_name">Name:</label><input type="text" '
+            'name="name" maxlength="20" required id="id_name"></div>',
+        )
+
+    def test_orderfields2_form(self):
+        class OrderFields2(forms.ModelForm):
+            class Meta:
+                model = Category
+                fields = ["slug", "url", "name"]
+                exclude = ["url"]
+
+        self.assertEqual(list(OrderFields2.base_fields), ["slug", "name"])
+
+    def test_default_populated_on_optional_field(self):
+        class PubForm(forms.ModelForm):
+            mode = forms.CharField(max_length=255, required=False)
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ("mode",)
+
+        # Empty data uses the model field default.
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.mode, "di")
+        self.assertEqual(m1._meta.get_field("mode").get_default(), "di")
+
+        # Blank data doesn't use the model field default.
+        mf2 = PubForm({"mode": ""})
+        self.assertEqual(mf2.errors, {})
+        m2 = mf2.save(commit=False)
+        self.assertEqual(m2.mode, "")
+
+    def test_default_not_populated_on_non_empty_value_in_cleaned_data(self):
+        class PubForm(forms.ModelForm):
+            mode = forms.CharField(max_length=255, required=False)
+            mocked_mode = None
+
+            def clean(self):
+                self.cleaned_data["mode"] = self.mocked_mode
+                return self.cleaned_data
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ("mode",)
+
+        pub_form = PubForm({})
+        pub_form.mocked_mode = "de"
+        pub = pub_form.save(commit=False)
+        self.assertEqual(pub.mode, "de")
+        # Default should be populated on an empty value in cleaned_data.
+        default_mode = "di"
+        for empty_value in pub_form.fields["mode"].empty_values:
+            with self.subTest(empty_value=empty_value):
+                pub_form = PubForm({})
+                pub_form.mocked_mode = empty_value
+                pub = pub_form.save(commit=False)
+                self.assertEqual(pub.mode, default_mode)
+
+    def test_default_not_populated_on_optional_checkbox_input(self):
+        class PubForm(forms.ModelForm):
+            class Meta:
+                model = PublicationDefaults
+                fields = ("active",)
+
+        # Empty data doesn't use the model default because CheckboxInput
+        # doesn't have a value in HTML form submission.
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertIs(m1.active, False)
+        self.assertIsInstance(mf1.fields["active"].widget, forms.CheckboxInput)
+        self.assertIs(m1._meta.get_field("active").get_default(), True)
+
+    def test_default_not_populated_on_checkboxselectmultiple(self):
+        class PubForm(forms.ModelForm):
+            mode = forms.CharField(required=False, widget=forms.CheckboxSelectMultiple)
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ("mode",)
+
+        # Empty data doesn't use the model default because an unchecked
+        # CheckboxSelectMultiple doesn't have a value in HTML form submission.
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.mode, "")
+        self.assertEqual(m1._meta.get_field("mode").get_default(), "di")
+
+    def test_default_not_populated_on_selectmultiple(self):
+        class PubForm(forms.ModelForm):
+            mode = forms.CharField(required=False, widget=forms.SelectMultiple)
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ("mode",)
+
+        # Empty data doesn't use the model default because an unselected
+        # SelectMultiple doesn't have a value in HTML form submission.
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.mode, "")
+        self.assertEqual(m1._meta.get_field("mode").get_default(), "di")
+
+    def test_prefixed_form_with_default_field(self):
+        class PubForm(forms.ModelForm):
+            prefix = "form-prefix"
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ("mode",)
+
+        mode = "de"
+        self.assertNotEqual(
+            mode, PublicationDefaults._meta.get_field("mode").get_default()
+        )
+
+        mf1 = PubForm({"form-prefix-mode": mode})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.mode, mode)
+
+    def test_renderer_kwarg(self):
+        custom = object()
+        self.assertIs(ProductForm(renderer=custom).renderer, custom)
+
+    def test_default_splitdatetime_field(self):
+        class PubForm(forms.ModelForm):
+            datetime_published = forms.SplitDateTimeField(required=False)
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ("datetime_published",)
+
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.datetime_published, datetime.datetime(2000, 1, 1))
+
+        mf2 = PubForm(
+            {"datetime_published_0": "2010-01-01", "datetime_published_1": "0:00:00"}
+        )
+        self.assertEqual(mf2.errors, {})
+        m2 = mf2.save(commit=False)
+        self.assertEqual(m2.datetime_published, datetime.datetime(2010, 1, 1))
+
+    def test_default_filefield(self):
+        class PubForm(forms.ModelForm):
+            class Meta:
+                model = PublicationDefaults
+                fields = ("file",)
+
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.file.name, "default.txt")
+
+        mf2 = PubForm({}, {"file": SimpleUploadedFile("name", b"foo")})
+        self.assertEqual(mf2.errors, {})
+        m2 = mf2.save(commit=False)
+        self.assertEqual(m2.file.name, "name")
+
+    def test_default_selectdatewidget(self):
+        class PubForm(forms.ModelForm):
+            date_published = forms.DateField(
+                required=False, widget=forms.SelectDateWidget
+            )
+
+            class Meta:
+                model = PublicationDefaults
+                fields = ("date_published",)
+
+        mf1 = PubForm({})
+        self.assertEqual(mf1.errors, {})
+        m1 = mf1.save(commit=False)
+        self.assertEqual(m1.date_published, datetime.date.today())
+
+        mf2 = PubForm(
+            {
+                "date_published_year": "2010",
+                "date_published_month": "1",
+                "date_published_day": "1",
+            }
+        )
+        self.assertEqual(mf2.errors, {})
+        m2 = mf2.save(commit=False)
+        self.assertEqual(m2.date_published, datetime.date(2010, 1, 1))
+
+
+# RemovedInDjango60Warning.
+# It's a temporary workaround for the deprecation period.
+class HttpsURLField(forms.URLField):
+    def __init__(self, **kwargs):
+        super().__init__(assume_scheme="https", **kwargs)
+
+
+class FieldOverridesByFormMetaForm(forms.ModelForm):
+    class Meta:
+        model = Category
+        fields = ["name", "url", "slug"]
+        widgets = {
+            "name": forms.Textarea,
+            "url": forms.TextInput(attrs={"class": "url"}),
+        }
+        labels = {
+            "name": "Title",
+        }
+        help_texts = {
+            "slug": "Watch out! Letters, numbers, underscores and hyphens only.",
+        }
+        error_messages = {
+            "slug": {
+                "invalid": (
+                    "Didn't you read the help text? "
+                    "We said letters, numbers, underscores and hyphens only!"
+                )
+            }
+        }
+        field_classes = {
+            "url": HttpsURLField,
+        }
+
+
+class TestFieldOverridesByFormMeta(SimpleTestCase):
+    def test_widget_overrides(self):
+        form = FieldOverridesByFormMetaForm()
+        self.assertHTMLEqual(
+            str(form["name"]),
+            '<textarea id="id_name" rows="10" cols="40" name="name" maxlength="20" '
+            "required></textarea>",
+        )
+        self.assertHTMLEqual(
+            str(form["url"]),
+            '<input id="id_url" type="text" class="url" name="url" maxlength="40" '
+            "required>",
+        )
+        self.assertHTMLEqual(
+            str(form["slug"]),
+            '<input id="id_slug" type="text" name="slug" maxlength="20" '
+            'aria-describedby="id_slug_helptext" required>',
+        )
+
+    def test_label_overrides(self):
+        form = FieldOverridesByFormMetaForm()
+        self.assertHTMLEqual(
+            str(form["name"].label_tag()),
+            '<label for="id_name">Title:</label>',
+        )
+        self.assertHTMLEqual(
+            str(form["url"].label_tag()),
+            '<label for="id_url">The URL:</label>',
+        )
+        self.assertHTMLEqual(
+            str(form["slug"].label_tag()),
+            '<label for="id_slug">Slug:</label>',
+        )
+        self.assertHTMLEqual(
+            form["name"].legend_tag(),
+            '<legend for="id_name">Title:</legend>',
+        )
+        self.assertHTMLEqual(
+            form["url"].legend_tag(),
+            '<legend for="id_url">The URL:</legend>',
+        )
+        self.assertHTMLEqual(
+            form["slug"].legend_tag(),
+            '<legend for="id_slug">Slug:</legend>',
+        )
+
+    def test_help_text_overrides(self):
+        form = FieldOverridesByFormMetaForm()
+        self.assertEqual(
+            form["slug"].help_text,
+            "Watch out! Letters, numbers, underscores and hyphens only.",
+        )
+
+    def test_error_messages_overrides(self):
+        form = FieldOverridesByFormMetaForm(
+            data={
+                "name": "Category",
+                "url": "http://www.example.com/category/",
+                "slug": "!%#*@",
+            }
+        )
+        form.full_clean()
+
+        error = [
+            "Didn't you read the help text? "
+            "We said letters, numbers, underscores and hyphens only!",
+        ]
+        self.assertEqual(form.errors, {"slug": error})
+
+    def test_field_type_overrides(self):
+        form = FieldOverridesByFormMetaForm()
+        self.assertIs(Category._meta.get_field("url").__class__, models.CharField)
+        self.assertIsInstance(form.fields["url"], forms.URLField)
+
+
+class IncompleteCategoryFormWithFields(forms.ModelForm):
+    """
+    A form that replaces the model's url field with a custom one. This should
+    prevent the model field's validation from being called.
+    """
+
+    url = forms.CharField(required=False)
+
+    class Meta:
+        fields = ("name", "slug")
+        model = Category
+
+
+class IncompleteCategoryFormWithExclude(forms.ModelForm):
+    """
+    A form that replaces the model's url field with a custom one. This should
+    prevent the model field's validation from being called.
+    """
+
+    url = forms.CharField(required=False)
+
+    class Meta:
+        exclude = ["url"]
+        model = Category
+
+
+class ValidationTest(SimpleTestCase):
+    def test_validates_with_replaced_field_not_specified(self):
+        form = IncompleteCategoryFormWithFields(
+            data={"name": "some name", "slug": "some-slug"}
+        )
+        self.assertIs(form.is_valid(), True)
+
+    def test_validates_with_replaced_field_excluded(self):
+        form = IncompleteCategoryFormWithExclude(
+            data={"name": "some name", "slug": "some-slug"}
+        )
+        self.assertIs(form.is_valid(), True)
+
+    def test_notrequired_overrides_notblank(self):
+        form = CustomWriterForm({})
+        self.assertIs(form.is_valid(), True)
+
+
+class UniqueTest(TestCase):
+    """
+    unique/unique_together validation.
+    """
+
+    @classmethod
+    def setUpTestData(cls):
+        cls.writer = Writer.objects.create(name="Mike Royko")
+
+    def test_simple_unique(self):
+        form = ProductForm({"slug": "teddy-bear-blue"})
+        self.assertTrue(form.is_valid())
+        obj = form.save()
+        form = ProductForm({"slug": "teddy-bear-blue"})
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["slug"], ["Product with this Slug already exists."]
+        )
+        form = ProductForm({"slug": "teddy-bear-blue"}, instance=obj)
+        self.assertTrue(form.is_valid())
+
+    def test_unique_together(self):
+        """ModelForm test of unique_together constraint"""
+        form = PriceForm({"price": "6.00", "quantity": "1"})
+        self.assertTrue(form.is_valid())
+        form.save()
+        form = PriceForm({"price": "6.00", "quantity": "1"})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["__all__"],
+            ["Price with this Price and Quantity already exists."],
+        )
+
+    def test_unique_together_exclusion(self):
+        """
+        Forms don't validate unique_together constraints when only part of the
+        constraint is included in the form's fields. This allows using
+        form.save(commit=False) and then assigning the missing field(s) to the
+        model instance.
+        """
+
+        class BookForm(forms.ModelForm):
+            class Meta:
+                model = DerivedBook
+                fields = ("isbn", "suffix1")
+
+        # The unique_together is on suffix1/suffix2 but only suffix1 is part
+        # of the form. The fields must have defaults, otherwise they'll be
+        # skipped by other logic.
+        self.assertEqual(DerivedBook._meta.unique_together, (("suffix1", "suffix2"),))
+        for name in ("suffix1", "suffix2"):
+            with self.subTest(name=name):
+                field = DerivedBook._meta.get_field(name)
+                self.assertEqual(field.default, 0)
+
+        # The form fails validation with "Derived book with this Suffix1 and
+        # Suffix2 already exists." if the unique_together validation isn't
+        # skipped.
+        DerivedBook.objects.create(isbn="12345")
+        form = BookForm({"isbn": "56789", "suffix1": "0"})
+        self.assertTrue(form.is_valid(), form.errors)
+
+    def test_multiple_field_unique_together(self):
+        """
+        When the same field is involved in multiple unique_together
+        constraints, we need to make sure we don't remove the data for it
+        before doing all the validation checking (not just failing after
+        the first one).
+        """
+
+        class TripleForm(forms.ModelForm):
+            class Meta:
+                model = Triple
+                fields = "__all__"
+
+        Triple.objects.create(left=1, middle=2, right=3)
+
+        form = TripleForm({"left": "1", "middle": "2", "right": "3"})
+        self.assertFalse(form.is_valid())
+
+        form = TripleForm({"left": "1", "middle": "3", "right": "1"})
+        self.assertTrue(form.is_valid())
+
+    @skipUnlessDBFeature("supports_nullable_unique_constraints")
+    def test_unique_null(self):
+        title = "I May Be Wrong But I Doubt It"
+        form = BookForm({"title": title, "author": self.writer.pk})
+        self.assertTrue(form.is_valid())
+        form.save()
+        form = BookForm({"title": title, "author": self.writer.pk})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["__all__"], ["Book with this Title and Author already exists."]
+        )
+        form = BookForm({"title": title})
+        self.assertTrue(form.is_valid())
+        form.save()
+        form = BookForm({"title": title})
+        self.assertTrue(form.is_valid())
+
+    def test_inherited_unique(self):
+        title = "Boss"
+        Book.objects.create(title=title, author=self.writer, special_id=1)
+        form = DerivedBookForm(
+            {
+                "title": "Other",
+                "author": self.writer.pk,
+                "special_id": "1",
+                "isbn": "12345",
+            }
+        )
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["special_id"], ["Book with this Special id already exists."]
+        )
+
+    def test_inherited_unique_together(self):
+        title = "Boss"
+        form = BookForm({"title": title, "author": self.writer.pk})
+        self.assertTrue(form.is_valid())
+        form.save()
+        form = DerivedBookForm(
+            {"title": title, "author": self.writer.pk, "isbn": "12345"}
+        )
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["__all__"], ["Book with this Title and Author already exists."]
+        )
+
+    def test_abstract_inherited_unique(self):
+        title = "Boss"
+        isbn = "12345"
+        DerivedBook.objects.create(title=title, author=self.writer, isbn=isbn)
+        form = DerivedBookForm(
+            {
+                "title": "Other",
+                "author": self.writer.pk,
+                "isbn": isbn,
+                "suffix1": "1",
+                "suffix2": "2",
+            }
+        )
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["isbn"], ["Derived book with this Isbn already exists."]
+        )
+
+    def test_abstract_inherited_unique_together(self):
+        title = "Boss"
+        isbn = "12345"
+        DerivedBook.objects.create(title=title, author=self.writer, isbn=isbn)
+        form = DerivedBookForm(
+            {
+                "title": "Other",
+                "author": self.writer.pk,
+                "isbn": "9876",
+                "suffix1": "0",
+                "suffix2": "0",
+            }
+        )
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["__all__"],
+            ["Derived book with this Suffix1 and Suffix2 already exists."],
+        )
+
+    def test_explicitpk_unspecified(self):
+        """Test for primary_key being in the form and failing validation."""
+        form = ExplicitPKForm({"key": "", "desc": ""})
+        self.assertFalse(form.is_valid())
+
+    def test_explicitpk_unique(self):
+        """Ensure keys and blank character strings are tested for uniqueness."""
+        form = ExplicitPKForm({"key": "key1", "desc": ""})
+        self.assertTrue(form.is_valid())
+        form.save()
+        form = ExplicitPKForm({"key": "key1", "desc": ""})
+        self.assertFalse(form.is_valid())
+        if connection.features.interprets_empty_strings_as_nulls:
+            self.assertEqual(len(form.errors), 1)
+            self.assertEqual(
+                form.errors["key"], ["Explicit pk with this Key already exists."]
+            )
+        else:
+            self.assertEqual(len(form.errors), 3)
+            self.assertEqual(
+                form.errors["__all__"],
+                ["Explicit pk with this Key and Desc already exists."],
+            )
+            self.assertEqual(
+                form.errors["desc"], ["Explicit pk with this Desc already exists."]
+            )
+            self.assertEqual(
+                form.errors["key"], ["Explicit pk with this Key already exists."]
+            )
+
+    def test_unique_for_date(self):
+        p = Post.objects.create(
+            title="Django 1.0 is released",
+            slug="Django 1.0",
+            subtitle="Finally",
+            posted=datetime.date(2008, 9, 3),
+        )
+        form = PostForm({"title": "Django 1.0 is released", "posted": "2008-09-03"})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["title"], ["Title must be unique for Posted date."]
+        )
+        form = PostForm({"title": "Work on Django 1.1 begins", "posted": "2008-09-03"})
+        self.assertTrue(form.is_valid())
+        form = PostForm({"title": "Django 1.0 is released", "posted": "2008-09-04"})
+        self.assertTrue(form.is_valid())
+        form = PostForm({"slug": "Django 1.0", "posted": "2008-01-01"})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(form.errors["slug"], ["Slug must be unique for Posted year."])
+        form = PostForm({"subtitle": "Finally", "posted": "2008-09-30"})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(
+            form.errors["subtitle"], ["Subtitle must be unique for Posted month."]
+        )
+        data = {
+            "subtitle": "Finally",
+            "title": "Django 1.0 is released",
+            "slug": "Django 1.0",
+            "posted": "2008-09-03",
+        }
+        form = PostForm(data, instance=p)
+        self.assertTrue(form.is_valid())
+        form = PostForm({"title": "Django 1.0 is released"})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(form.errors["posted"], ["This field is required."])
+
+    def test_unique_for_date_in_exclude(self):
+        """
+        If the date for unique_for_* constraints is excluded from the
+        ModelForm (in this case 'posted' has editable=False, then the
+        constraint should be ignored.
+        """
+
+        class DateTimePostForm(forms.ModelForm):
+            class Meta:
+                model = DateTimePost
+                fields = "__all__"
+
+        DateTimePost.objects.create(
+            title="Django 1.0 is released",
+            slug="Django 1.0",
+            subtitle="Finally",
+            posted=datetime.datetime(2008, 9, 3, 10, 10, 1),
+        )
+        # 'title' has unique_for_date='posted'
+        form = DateTimePostForm(
+            {"title": "Django 1.0 is released", "posted": "2008-09-03"}
+        )
+        self.assertTrue(form.is_valid())
+        # 'slug' has unique_for_year='posted'
+        form = DateTimePostForm({"slug": "Django 1.0", "posted": "2008-01-01"})
+        self.assertTrue(form.is_valid())
+        # 'subtitle' has unique_for_month='posted'
+        form = DateTimePostForm({"subtitle": "Finally", "posted": "2008-09-30"})
+        self.assertTrue(form.is_valid())
+
+    def test_inherited_unique_for_date(self):
+        p = Post.objects.create(
+            title="Django 1.0 is released",
+            slug="Django 1.0",
+            subtitle="Finally",
+            posted=datetime.date(2008, 9, 3),
+        )
+        form = DerivedPostForm(
+            {"title": "Django 1.0 is released", "posted": "2008-09-03"}
+        )
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["title"], ["Title must be unique for Posted date."]
+        )
+        form = DerivedPostForm(
+            {"title": "Work on Django 1.1 begins", "posted": "2008-09-03"}
+        )
+        self.assertTrue(form.is_valid())
+        form = DerivedPostForm(
+            {"title": "Django 1.0 is released", "posted": "2008-09-04"}
+        )
+        self.assertTrue(form.is_valid())
+        form = DerivedPostForm({"slug": "Django 1.0", "posted": "2008-01-01"})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(form.errors["slug"], ["Slug must be unique for Posted year."])
+        form = DerivedPostForm({"subtitle": "Finally", "posted": "2008-09-30"})
+        self.assertFalse(form.is_valid())
+        self.assertEqual(
+            form.errors["subtitle"], ["Subtitle must be unique for Posted month."]
+        )
+        data = {
+            "subtitle": "Finally",
+            "title": "Django 1.0 is released",
+            "slug": "Django 1.0",
+            "posted": "2008-09-03",
+        }
+        form = DerivedPostForm(data, instance=p)
+        self.assertTrue(form.is_valid())
+
+    def test_unique_for_date_with_nullable_date(self):
+        class FlexDatePostForm(forms.ModelForm):
+            class Meta:
+                model = FlexibleDatePost
+                fields = "__all__"
+
+        p = FlexibleDatePost.objects.create(
+            title="Django 1.0 is released",
+            slug="Django 1.0",
+            subtitle="Finally",
+            posted=datetime.date(2008, 9, 3),
+        )
+
+        form = FlexDatePostForm({"title": "Django 1.0 is released"})
+        self.assertTrue(form.is_valid())
+        form = FlexDatePostForm({"slug": "Django 1.0"})
+        self.assertTrue(form.is_valid())
+        form = FlexDatePostForm({"subtitle": "Finally"})
+        self.assertTrue(form.is_valid())
+        data = {
+            "subtitle": "Finally",
+            "title": "Django 1.0 is released",
+            "slug": "Django 1.0",
+        }
+        form = FlexDatePostForm(data, instance=p)
+        self.assertTrue(form.is_valid())
+
+    def test_override_unique_message(self):
+        class CustomProductForm(ProductForm):
+            class Meta(ProductForm.Meta):
+                error_messages = {
+                    "slug": {
+                        "unique": "%(model_name)s's %(field_label)s not unique.",
+                    }
+                }
+
+        Product.objects.create(slug="teddy-bear-blue")
+        form = CustomProductForm({"slug": "teddy-bear-blue"})
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(form.errors["slug"], ["Product's Slug not unique."])
+
+    def test_override_unique_together_message(self):
+        class CustomPriceForm(PriceForm):
+            class Meta(PriceForm.Meta):
+                error_messages = {
+                    NON_FIELD_ERRORS: {
+                        "unique_together": (
+                            "%(model_name)s's %(field_labels)s not unique."
+                        ),
+                    }
+                }
+
+        Price.objects.create(price=6.00, quantity=1)
+        form = CustomPriceForm({"price": "6.00", "quantity": "1"})
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors[NON_FIELD_ERRORS], ["Price's Price and Quantity not unique."]
+        )
+
+    def test_override_unique_for_date_message(self):
+        class CustomPostForm(PostForm):
+            class Meta(PostForm.Meta):
+                error_messages = {
+                    "title": {
+                        "unique_for_date": (
+                            "%(model_name)s's %(field_label)s not unique "
+                            "for %(date_field_label)s date."
+                        ),
+                    }
+                }
+
+        Post.objects.create(
+            title="Django 1.0 is released",
+            slug="Django 1.0",
+            subtitle="Finally",
+            posted=datetime.date(2008, 9, 3),
+        )
+        form = CustomPostForm(
+            {"title": "Django 1.0 is released", "posted": "2008-09-03"}
+        )
+        self.assertEqual(len(form.errors), 1)
+        self.assertEqual(
+            form.errors["title"], ["Post's Title not unique for Posted date."]
+        )
+
+
+class ModelFormBasicTests(TestCase):
+    def create_basic_data(self):
+        self.c1 = Category.objects.create(
+            name="Entertainment", slug="entertainment", url="entertainment"
+        )
+        self.c2 = Category.objects.create(
+            name="It's a test", slug="its-test", url="test"
+        )
+        self.c3 = Category.objects.create(
+            name="Third test", slug="third-test", url="third"
+        )
+        self.w_royko = Writer.objects.create(name="Mike Royko")
+        self.w_woodward = Writer.objects.create(name="Bob Woodward")
+
+    def test_base_form(self):
+        self.assertEqual(Category.objects.count(), 0)
+        f = BaseCategoryForm()
+        self.assertHTMLEqual(
+            str(f),
+            '<div><label for="id_name">Name:</label><input type="text" name="name" '
+            'maxlength="20" required id="id_name"></div><div><label for="id_slug">Slug:'
+            '</label><input type="text" name="slug" maxlength="20" required '
+            'id="id_slug"></div><div><label for="id_url">The URL:</label>'
+            '<input type="text" name="url" maxlength="40" required id="id_url"></div>',
+        )
+        self.assertHTMLEqual(
+            str(f.as_ul()),
+            """
+            <li><label for="id_name">Name:</label>
+            <input id="id_name" type="text" name="name" maxlength="20" required></li>
+            <li><label for="id_slug">Slug:</label>
+            <input id="id_slug" type="text" name="slug" maxlength="20" required></li>
+            <li><label for="id_url">The URL:</label>
+            <input id="id_url" type="text" name="url" maxlength="40" required></li>
+            """,
+        )
+        self.assertHTMLEqual(
+            str(f["name"]),
+            """<input id="id_name" type="text" name="name" maxlength="20" required>""",
+        )
+
+    def test_auto_id(self):
+        f = BaseCategoryForm(auto_id=False)
+        self.assertHTMLEqual(
+            str(f.as_ul()),
+            """<li>Name: <input type="text" name="name" maxlength="20" required></li>
+<li>Slug: <input type="text" name="slug" maxlength="20" required></li>
+<li>The URL: <input type="text" name="url" maxlength="40" required></li>""",
+        )
+
+    def test_initial_values(self):
+        self.create_basic_data()
+        # Initial values can be provided for model forms
+        f = ArticleForm(
+            auto_id=False,
+            initial={
+                "headline": "Your headline here",
+                "categories": [str(self.c1.id), str(self.c2.id)],
+            },
+        )
+        self.assertHTMLEqual(
+            f.as_ul(),
+            """
+            <li>Headline:
+            <input type="text" name="headline" value="Your headline here" maxlength="50"
+                required>
+            </li>
+            <li>Slug: <input type="text" name="slug" maxlength="50" required></li>
+            <li>Pub date: <input type="text" name="pub_date" required></li>
+            <li>Writer: <select name="writer" required>
+            <option value="" selected>---------</option>
+            <option value="%s">Bob Woodward</option>
+            <option value="%s">Mike Royko</option>
+            </select></li>
+            <li>Article:
+            <textarea rows="10" cols="40" name="article" required></textarea></li>
+            <li>Categories: <select multiple name="categories">
+            <option value="%s" selected>Entertainment</option>
+            <option value="%s" selected>It&#x27;s a test</option>
+            <option value="%s">Third test</option>
+            </select></li>
+            <li>Status: <select name="status">
+            <option value="" selected>---------</option>
+            <option value="1">Draft</option>
+            <option value="2">Pending</option>
+            <option value="3">Live</option>
+            </select></li>
+            """
+            % (self.w_woodward.pk, self.w_royko.pk, self.c1.pk, self.c2.pk, self.c3.pk),
+        )
+
+        # When the ModelForm is passed an instance, that instance's current values are
+        # inserted as 'initial' data in each Field.
+        f = RoykoForm(auto_id=False, instance=self.w_royko)
+        self.assertHTMLEqual(
+            str(f),
+            '<div>Name:<div class="helptext">Use both first and last names.</div>'
+            '<input type="text" name="name" value="Mike Royko" maxlength="50" '
+            "required></div>",
+        )
+
+        art = Article.objects.create(
+            headline="Test article",
+            slug="test-article",
+            pub_date=datetime.date(1988, 1, 4),
+            writer=self.w_royko,
+            article="Hello.",
+        )
+        art_id_1 = art.id
+
+        f = ArticleForm(auto_id=False, instance=art)
+        self.assertHTMLEqual(
+            f.as_ul(),
+            """
+            <li>Headline:
+            <input type="text" name="headline" value="Test article" maxlength="50"
+                required>
+            </li>
+            <li>Slug:
+            <input type="text" name="slug" value="test-article" maxlength="50" required>
+            </li>
+            <li>Pub date:
+            <input type="text" name="pub_date" value="1988-01-04" required></li>
+            <li>Writer: <select name="writer" required>
+            <option value="">---------</option>
+            <option value="%s">Bob Woodward</option>
+            <option value="%s" selected>Mike Royko</option>
+            </select></li>
+            <li>Article:
+            <textarea rows="10" cols="40" name="article" required>Hello.</textarea></li>
+            <li>Categories: <select multiple name="categories">
+            <option value="%s">Entertainment</option>
+            <option value="%s">It&#x27;s a test</option>
+            <option value="%s">Third test</option>
+            </select></li>
+            <li>Status: <select name="status">
+            <option value="" selected>---------</option>
+            <option value="1">Draft</option>
+            <option value="2">Pending</option>
+            <option value="3">Live</option>
+            </select></li>
+            """
+            % (self.w_woodward.pk, self.w_royko.pk, self.c1.pk, self.c2.pk, self.c3.pk),
+        )
+
+        f = ArticleForm(
+            {
+                "headline": "Test headline",
+                "slug": "test-headline",
+                "pub_date": "1984-02-06",
+                "writer": str(self.w_royko.pk),
+                "article": "Hello.",
+            },
+            instance=art,
+        )
+        self.assertEqual(f.errors, {})
+        self.assertTrue(f.is_valid())
+        test_art = f.save()
+        self.assertEqual(test_art.id, art_id_1)
+        test_art = Article.objects.get(id=art_id_1)
+        self.assertEqual(test_art.headline, "Test headline")
+
+    def test_m2m_initial_callable(self):
+        """
+        A callable can be provided as the initial value for an m2m field.
+        """
+        self.maxDiff = 1200
+        self.create_basic_data()
+
+        # Set up a callable initial value
+        def formfield_for_dbfield(db_field, **kwargs):
+            if db_field.name == "categories":
+                kwargs["initial"] = lambda: Category.objects.order_by("name")[:2]
+            return db_field.formfield(**kwargs)
+
+        # Create a ModelForm, instantiate it, and check that the output is as expected
+        ModelForm = modelform_factory(
+            Article,
+            fields=["headline", "categories"],
+            formfield_callback=formfield_for_dbfield,
+        )
+        form = ModelForm()
+        self.assertHTMLEqual(
+            form.as_ul(),
+            """<li><label for="id_headline">Headline:</label>
+<input id="id_headline" type="text" name="headline" maxlength="50" required></li>
+<li><label for="id_categories">Categories:</label>
+<select multiple name="categories" id="id_categories">
+<option value="%d" selected>Entertainment</option>
+<option value="%d" selected>It&#x27;s a test</option>
+<option value="%d">Third test</option>
+</select></li>"""
+            % (self.c1.pk, self.c2.pk, self.c3.pk),
+        )
+
+    def test_basic_creation(self):
+        self.assertEqual(Category.objects.count(), 0)
+        f = BaseCategoryForm(
+            {
+                "name": "Entertainment",
+                "slug": "entertainment",
+                "url": "entertainment",
+            }
+        )
+        self.assertTrue(f.is_valid())
+        self.assertEqual(f.cleaned_data["name"], "Entertainment")
+        self.assertEqual(f.cleaned_data["slug"], "entertainment")
+        self.assertEqual(f.cleaned_data["url"], "entertainment")
+        c1 = f.save()
+        # Testing whether the same object is returned from the
+        # ORM... not the fastest way...
+
+        self.assertEqual(Category.objects.count(), 1)
+        self.assertEqual(c1, Category.objects.all()[0])
+        self.assertEqual(c1.name, "Entertainment")
+
+    def test_save_commit_false(self):
+        # If you call save() with commit=False, then it will return an object that
+        # hasn't yet been saved to the database. In this case, it's up to you to call
+        # save() on the resulting model instance.
+        f = BaseCategoryForm(
+            {"name": "Third test", "slug": "third-test", "url": "third"}
+        )
+        self.assertTrue(f.is_valid())
+        c1 = f.save(commit=False)
+        self.assertEqual(c1.name, "Third test")
+        self.assertEqual(Category.objects.count(), 0)
+        c1.save()
+        self.assertEqual(Category.objects.count(), 1)
+
+    def test_save_with_data_errors(self):
+        # If you call save() with invalid data, you'll get a ValueError.
+        f = BaseCategoryForm({"name": "", "slug": "not a slug!", "url": "foo"})
+        self.assertEqual(f.errors["name"], ["This field is required."])
+        self.assertEqual(
+            f.errors["slug"],
+            [
+                "Enter a valid “slug” consisting of letters, numbers, underscores or "
+                "hyphens."
+            ],
+        )
+        self.assertEqual(f.cleaned_data, {"url": "foo"})
+        msg = "The Category could not be created because the data didn't validate."
+        with self.assertRaisesMessage(ValueError, msg):
+            f.save()
+        f = BaseCategoryForm({"name": "", "slug": "", "url": "foo"})
+        with self.assertRaisesMessage(ValueError, msg):
+            f.save()
+
+    def test_multi_fields(self):
+        self.create_basic_data()
+        self.maxDiff = None
+        # ManyToManyFields are represented by a MultipleChoiceField, ForeignKeys and any
+        # fields with the 'choices' attribute are represented by a ChoiceField.
+        f = ArticleForm(auto_id=False)
+        self.assertHTMLEqual(
+            str(f),
+            """
+            <div>Headline:
+                <input type="text" name="headline" maxlength="50" required>
+            </div>
+            <div>Slug:
+                <input type="text" name="slug" maxlength="50" required>
+            </div>
+            <div>Pub date:
+                <input type="text" name="pub_date" required>
+            </div>
+            <div>Writer:
+                <select name="writer" required>
+                    <option value="" selected>---------</option>
+                    <option value="%s">Bob Woodward</option>
+                    <option value="%s">Mike Royko</option>
+                </select>
+            </div>
+            <div>Article:
+                <textarea name="article" cols="40" rows="10" required></textarea>
+            </div>
+            <div>Categories:
+                <select name="categories" multiple>
+                    <option value="%s">Entertainment</option>
+                    <option value="%s">It&#x27;s a test</option>
+                    <option value="%s">Third test</option>
+                </select>
+            </div>
+            <div>Status:
+                <select name="status">
+                    <option value="" selected>---------</option>
+                    <option value="1">Draft</option><option value="2">Pending</option>
+                    <option value="3">Live</option>
+                </select>
+            </div>
+            """
+            % (self.w_woodward.pk, self.w_royko.pk, self.c1.pk, self.c2.pk, self.c3.pk),
+        )
+
+        # Add some categories and test the many-to-many form output.
+        new_art = Article.objects.create(
+            article="Hello.",
+            headline="New headline",
+            slug="new-headline",
+            pub_date=datetime.date(1988, 1, 4),
+            writer=self.w_royko,
+        )
+        new_art.categories.add(Category.objects.get(name="Entertainment"))
+        self.assertSequenceEqual(new_art.categories.all(), [self.c1])
+        f = ArticleForm(auto_id=False, instance=new_art)
+        self.assertHTMLEqual(
+            f.as_ul(),
+            """
+            <li>Headline:
+            <input type="text" name="headline" value="New headline" maxlength="50"
+                required>
+            </li>
+            <li>Slug:
+            <input type="text" name="slug" value="new-headline" maxlength="50" required>
+            </li>
+            <li>Pub date:
+            <input type="text" name="pub_date" value="1988-01-04" required></li>
+            <li>Writer: <select name="writer" required>
+            <option value="">---------</option>
+            <option value="%s">Bob Woodward</option>
+            <option value="%s" selected>Mike Royko</option>
+            </select></li>
+            <li>Article:
+            <textarea rows="10" cols="40" name="article" required>Hello.</textarea></li>
+            <li>Categories: <select multiple name="categories">
+            <option value="%s" selected>Entertainment</option>
+            <option value="%s">It&#x27;s a test</option>
+            <option value="%s">Third test</option>
+            </select></li>
+            <li>Status: <select name="status">
+            <option value="" selected>---------</option>
+            <option value="1">Draft</option>
+            <option value="2">Pending</option>
+            <option value="3">Live</option>
+            </select></li>
+            """
+            % (self.w_woodward.pk, self.w_royko.pk, self.c1.pk, self.c2.pk, self.c3.pk),
+        )
+
+    def test_subset_fields(self):
+        # You can restrict a form to a subset of the complete list of fields
+        # by providing a 'fields' argument. If you try to save a
+        # model created with such a form, you need to ensure that the fields
+        # that are _not_ on the form have default values, or are allowed to have
+        # a value of None. If a field isn't specified on a form, the object created
+        # from the form can't provide a value for that field!
+        class PartialArticleForm(forms.ModelForm):
+            class Meta:
+                model = Article
+                fields = ("headline", "pub_date")
+
+        f = PartialArticleForm(auto_id=False)
+        self.assertHTMLEqual(
+            str(f),
+            '<div>Headline:<input type="text" name="headline" maxlength="50" required>'
+            '</div><div>Pub date:<input type="text" name="pub_date" required></div>',
+        )
+
+        class PartialArticleFormWithSlug(forms.ModelForm):
+            class Meta:
+                model = Article
+                fields = ("headline", "slug", "pub_date")
+
+        w_royko = Writer.objects.create(name="Mike Royko")
+        art = Article.objects.create(
+            article="Hello.",
+            headline="New headline",
+            slug="new-headline",
+            pub_date=datetime.date(1988, 1, 4),
+            writer=w_royko,
+        )
+        f = PartialArticleFormWithSlug(
+            {
+                "headline": "New headline",
+                "slug": "new-headline",
+                "pub_date": "1988-01-04",
+            },
+            auto_id=False,
+            instance=art,
+        )
+        self.assertHTMLEqual(
+            f.as_ul(),
+            """
+            <li>Headline:
+            <input type="text" name="headline" value="New headline" maxlength="50"
+                required>
+            </li>
+            <li>Slug:
+            <input type="text" name="slug" value="new-headline" maxlength="50"
+                required>
+            </li>
+            <li>Pub date:
+            <input type="text" name="pub_date" value="1988-01-04" required></li>
+            """,
+        )
+        self.assertTrue(f.is_valid())
+        new_art = f.save()
+        self.assertEqual(new_art.id, art.id)
+        new_art = Article.objects.get(id=art.id)
+        self.assertEqual(new_art.headline, "New headline")
+
+    def test_m2m_editing(self):
+        self.create_basic_data()
+        form_data = {
+            "headline": "New headline",
+            "slug": "new-headline",
+            "pub_date": "1988-01-04",
+            "writer": str(self.w_royko.pk),
+            "article": "Hello.",
+            "categories": [str(self.c1.id), str(self.c2.id)],
+        }
+        # Create a new article, with categories, via the form.
+        f = ArticleForm(form_data)
+        new_art = f.save()
+        new_art = Article.objects.get(id=new_art.id)
+        art_id_1 = new_art.id
+        self.assertSequenceEqual(
+            new_art.categories.order_by("name"), [self.c1, self.c2]
+        )
+
+        # Now, submit form data with no categories. This deletes the existing
+        # categories.
+        form_data["categories"] = []
+        f = ArticleForm(form_data, instance=new_art)
+        new_art = f.save()
+        self.assertEqual(new_art.id, art_id_1)
+        new_art = Article.objects.get(id=art_id_1)
+        self.assertSequenceEqual(new_art.categories.all(), [])
+
+        # Create a new article, with no categories, via the form.
+        f = ArticleForm(form_data)
+        new_art = f.save()
+        art_id_2 = new_art.id
+        self.assertNotIn(art_id_2, (None, art_id_1))
+        new_art = Article.objects.get(id=art_id_2)
+        self.assertSequenceEqual(new_art.categories.all(), [])
+
+        # Create a new article, with categories, via the form, but use commit=False.
+        # The m2m data won't be saved until save_m2m() is invoked on the form.
+        form_data["categories"] = [str(self.c1.id), str(self.c2.id)]
+        f = ArticleForm(form_data)
+        new_art = f.save(commit=False)
+
+        # Manually save the instance
+        new_art.save()
+        art_id_3 = new_art.id
+        self.assertNotIn(art_id_3, (None, art_id_1, art_id_2))
+
+        # The instance doesn't have m2m data yet
+        new_art = Article.objects.get(id=art_id_3)
+        self.assertSequenceEqual(new_art.categories.all(), [])
+
+        # Save the m2m data on the form
+        f.save_m2m()
+        self.assertSequenceEqual(
+            new_art.categories.order_by("name"), [self.c1, self.c2]
+        )
+
+    def test_custom_form_fields(self):
+        # Here, we define a custom ModelForm. Because it happens to have the
+        # same fields as the Category model, we can just call the form's save()
+        # to apply its changes to an existing Category instance.
+        class ShortCategory(forms.ModelForm):
+            name = forms.CharField(max_length=5)
+            slug = forms.CharField(max_length=5)
+            url = forms.CharField(max_length=3)
+
+            class Meta:
+                model = Category
+                fields = "__all__"
+
+        cat = Category.objects.create(name="Third test")
+        form = ShortCategory(
+            {"name": "Third", "slug": "third", "url": "3rd"}, instance=cat
+        )
+        self.assertEqual(form.save().name, "Third")
+        self.assertEqual(Category.objects.get(id=cat.id).name, "Third")
+
+    def test_runtime_choicefield_populated(self):
+        self.maxDiff = None
+        # Here, we demonstrate that choices for a ForeignKey ChoiceField are determined
+        # at runtime, based on the data in the database when the form is displayed, not
+        # the data in the database when the form is instantiated.
+        self.create_basic_data()
+        f = ArticleForm(auto_id=False)
+        self.assertHTMLEqual(
+            f.as_ul(),
+            '<li>Headline: <input type="text" name="headline" maxlength="50" required>'
+            "</li>"
+            '<li>Slug: <input type="text" name="slug" maxlength="50" required></li>'
+            '<li>Pub date: <input type="text" name="pub_date" required></li>'
+            '<li>Writer: <select name="writer" required>'
+            '<option value="" selected>---------</option>'
+            '<option value="%s">Bob Woodward</option>'
+            '<option value="%s">Mike Royko</option>'
+            "</select></li>"
+            '<li>Article: <textarea rows="10" cols="40" name="article" required>'
+            "</textarea></li>"
+            '<li>Categories: <select multiple name="categories">'
+            '<option value="%s">Entertainment</option>'
+            '<option value="%s">It&#x27;s a test</option>'
+            '<option value="%s">Third test</option>'
+            "</select> </li>"
+            '<li>Status: <select name="status">'
+            '<option value="" selected>---------</option>'
+            '<option value="1">Draft</option>'
+            '<option value="2">Pending</option>'
+            '<option value="3">Live</option>'
+            "</select></li>"
+            % (self.w_woodward.pk, self.w_royko.pk, self.c1.pk, self.c2.pk, self.c3.pk),
+        )
+
+        c4 = Category.objects.create(name="Fourth", url="4th")
+        w_bernstein = Writer.objects.create(name="Carl Bernstein")
+        self.assertHTMLEqual(
+            f.as_ul(),
+            '<li>Headline: <input type="text" name="headline" maxlength="50" required>'
+            "</li>"
+            '<li>Slug: <input type="text" name="slug" maxlength="50" required></li>'
+            '<li>Pub date: <input type="text" name="pub_date" required></li>'
+            '<li>Writer: <select name="writer" required>'
+            '<option value="" selected>---------</option>'
+            '<option value="%s">Bob Woodward</option>'
+            '<option value="%s">Carl Bernstein</option>'
+            '<option value="%s">Mike Royko</option>'
+            "</select></li>"
+            '<li>Article: <textarea rows="10" cols="40" name="article" required>'
+            "</textarea></li>"
+            '<li>Categories: <select multiple name="categories">'
+            '<option value="%s">Entertainment</option>'
+            '<option value="%s">It&#x27;s a test</option>'
+            '<option value="%s">Third test</option>'
+            '<option value="%s">Fourth</option>'
+            "</select></li>"
+            '<li>Status: <select name="status">'
+            '<option value="" selected>---------</option>'
+            '<option value="1">Draft</option>'
+            '<option value="2">Pending</option>'
+            '<option value="3">Live</option>'
+            "</select></li>"
+            % (
+                self.w_woodward.pk,
+                w_bernstein.pk,
+                self.w_royko.pk,
+                self.c1.pk,
+                self.c2.pk,
+                self.c3.pk,
+                c4.pk,
+            ),
+        )
+
+    def test_recleaning_model_form_instance(self):
+        """
+        Re-cleaning an instance that was added via a ModelForm shouldn't raise
+        a pk uniqueness error.
+        """
+
+        class AuthorForm(forms.ModelForm):
+            class Meta:
+                model = Author
+                fields = "__all__"
+
+        form = AuthorForm({"full_name": "Bob"})
+        self.assertTrue(form.is_valid())
+        obj = form.save()
+        obj.name = "Alice"
+        obj.full_clean()
+
+    def test_validate_foreign_key_uses_default_manager(self):
+        class MyForm(forms.ModelForm):
+            class Meta:
+                model = Article
+                fields = "__all__"
+
+        # Archived writers are filtered out by the default manager.
+        w = Writer.objects.create(name="Randy", archived=True)
+        data = {
+            "headline": "My Article",
+            "slug": "my-article",
+            "pub_date": datetime.date.today(),
+            "writer": w.pk,
+            "article": "lorem ipsum",
+        }
+        form = MyForm(data)
+        self.assertIs(form.is_valid(), False)
+        self.assertEqual(
+            form.errors,
+            {
+                "writer": [
+                    "Select a valid choice. That choice is not one of the available "
+                    "choices."
+                ]
+            },
+        )
+
+    def test_validate_foreign_key_to_model_with_overridden_manager(self):
+        class MyForm(forms.ModelForm):
+            class Meta:
+                model = Article
+                fields = "__all__"
+
+            def __init__(self, *args, **kwargs):
+                super().__init__(*args, **kwargs)
+                # Allow archived authors.
+                self.fields["writer"].queryset = Writer._base_manager.all()
+
+        w = Writer.objects.create(name="Randy", archived=True)
+        data = {
+            "headline": "My Article",
+            "slug": "my-article",
+            "pub_date": datetime.date.today(),
+            "writer": w.pk,
+            "article": "lorem ipsum",
+        }
+        form = MyForm(data)
+        self.assertIs(form.is_valid(), True)
+        article = form.save()
+        self.assertEqual(article.writer, w)
+
+
+class ModelMultipleChoiceFieldTests(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.c1 = Category.objects.create(
+            name="Entertainment", slug="entertainment", url="entertainment"
+        )
+        cls.c2 = Category.objects.create(
+            name="It's a test", slug="its-test", url="test"
+        )
+        cls.c3 = Category.objects.create(name="Third", slug="third-test", url="third")
+
+    def test_model_multiple_choice_field(self):
+        f = forms.ModelMultipleChoiceField(Category.objects.all())
+        self.assertCountEqual(
+            list(f.choices),
+            [
+                (self.c1.pk, "Entertainment"),
+                (self.c2.pk, "It's a test"),
+                (self.c3.pk, "Third"),
+            ],
+        )
+        with self.assertRaises(ValidationError):
+            f.clean(None)
+        with self.assertRaises(ValidationError):
+            f.clean([])
+        self.assertCountEqual(f.clean([self.c1.id]), [self.c1])
+        self.assertCountEqual(f.clean([self.c2.id]), [self.c2])
+        self.assertCountEqual(f.clean([str(self.c1.id)]), [self.c1])
+        self.assertCountEqual(
+            f.clean([str(self.c1.id), str(self.c2.id)]),
+            [self.c1, self.c2],
+        )
+        self.assertCountEqual(
+            f.clean([self.c1.id, str(self.c2.id)]),
+            [self.c1, self.c2],
+        )
+        self.assertCountEqual(
+            f.clean((self.c1.id, str(self.c2.id))),
+            [self.c1, self.c2],
+        )
+        with self.assertRaises(ValidationError):
+            f.clean(["0"])
+        with self.assertRaises(ValidationError):
+            f.clean("hello")
+        with self.assertRaises(ValidationError):
+            f.clean(["fail"])
+
+        # Invalid types that require TypeError to be caught (#22808).
+        with self.assertRaises(ValidationError):
+            f.clean([["fail"]])
+        with self.assertRaises(ValidationError):
+            f.clean([{"foo": "bar"}])
+
+        # Add a Category object *after* the ModelMultipleChoiceField has already been
+        # instantiated. This proves clean() checks the database during clean() rather
+        # than caching it at time of instantiation.
+        # Note, we are using an id of 1006 here since tests that run before
+        # this may create categories with primary keys up to 6. Use
+        # a number that will not conflict.
+        c6 = Category.objects.create(id=1006, name="Sixth", url="6th")
+        self.assertCountEqual(f.clean([c6.id]), [c6])
+
+        # Delete a Category object *after* the ModelMultipleChoiceField has already been
+        # instantiated. This proves clean() checks the database during clean() rather
+        # than caching it at time of instantiation.
+        Category.objects.get(url="6th").delete()
+        with self.assertRaises(ValidationError):
+            f.clean([c6.id])
+
+    def test_model_multiple_choice_required_false(self):
+        f = forms.ModelMultipleChoiceField(Category.objects.all(), required=False)
+        self.assertIsInstance(f.clean([]), EmptyQuerySet)
+        self.assertIsInstance(f.clean(()), EmptyQuerySet)
+        with self.assertRaises(ValidationError):
+            f.clean(["0"])
+        with self.assertRaises(ValidationError):
+            f.clean([str(self.c3.id), "0"])
+        with self.assertRaises(ValidationError):
+            f.clean([str(self.c1.id), "0"])
+
+        # queryset can be changed after the field is created.
+        f.queryset = Category.objects.exclude(name="Third")
+        self.assertCountEqual(
+            list(f.choices),
+            [(self.c1.pk, "Entertainment"), (self.c2.pk, "It's a test")],
+        )
+        self.assertSequenceEqual(f.clean([self.c2.id]), [self.c2])
+        with self.assertRaises(ValidationError):
+            f.clean([self.c3.id])
+        with self.assertRaises(ValidationError):
+            f.clean([str(self.c2.id), str(self.c3.id)])
+
+        f.queryset = Category.objects.all()
+        f.label_from_instance = lambda obj: "multicategory " + str(obj)
+        self.assertCountEqual(
+            list(f.choices),
+            [
+                (self.c1.pk, "multicategory Entertainment"),
+                (self.c2.pk, "multicategory It's a test"),
+                (self.c3.pk, "multicategory Third"),
+            ],
+        )
+
+    def test_model_multiple_choice_number_of_queries(self):
+        """
+        ModelMultipleChoiceField does O(1) queries instead of O(n) (#10156).
+        """
+        persons = [Writer.objects.create(name="Person %s" % i) for i in range(30)]
+
+        f = forms.ModelMultipleChoiceField(queryset=Writer.objects.all())
+        self.assertNumQueries(1, f.clean, [p.pk for p in persons[1:11:2]])
+
+    def test_model_multiple_choice_run_validators(self):
+        """
+        ModelMultipleChoiceField run given validators (#14144).
+        """
+        for i in range(30):
+            Writer.objects.create(name="Person %s" % i)
+
+        self._validator_run = False
+
+        def my_validator(value):
+            self._validator_run = True
+
+        f = forms.ModelMultipleChoiceField(
+            queryset=Writer.objects.all(), validators=[my_validator]
+        )
+        f.clean([p.pk for p in Writer.objects.all()[8:9]])
+        self.assertTrue(self._validator_run)
+
+    def test_model_multiple_choice_show_hidden_initial(self):
+        """
+        Test support of show_hidden_initial by ModelMultipleChoiceField.
+        """
+
+        class WriterForm(forms.Form):
+            persons = forms.ModelMultipleChoiceField(
+                show_hidden_initial=True, queryset=Writer.objects.all()
+            )
+
+        person1 = Writer.objects.create(name="Person 1")
+        person2 = Writer.objects.create(name="Person 2")
+
+        form = WriterForm(
+            initial={"persons": [person1, person2]},
+            data={
+                "initial-persons": [str(person1.pk), str(person2.pk)],
+                "persons": [str(person1.pk), str(person2.pk)],
+            },
+        )
+        self.assertTrue(form.is_valid())
+        self.assertFalse(form.has_changed())
+
+        form = WriterForm(
+            initial={"persons": [person1, person2]},
+            data={
+                "initial-persons": [str(person1.pk), str(person2.pk)],
+                "persons": [str(person2.pk)],
+            },
+        )
+        self.assertTrue(form.is_valid())
+        self.assertTrue(form.has_changed())
+
+    def test_model_multiple_choice_field_22745(self):
+        """
+        #22745 -- Make sure that ModelMultipleChoiceField with
+        CheckboxSelectMultiple widget doesn't produce unnecessary db queries
+        when accessing its BoundField's attrs.
+        """
+
+        class ModelMultipleChoiceForm(forms.Form):
+            categories = forms.ModelMultipleChoiceField(
+                Category.objects.all(), widget=forms.CheckboxSelectMultiple
+            )
+
+        form = ModelMultipleChoiceForm()
+        field = form["categories"]  # BoundField
+        template = Template("{{ field.name }}{{ field }}{{ field.help_text }}")
+        with self.assertNumQueries(1):
+            template.render(Context({"field": field}))
+
+    def test_show_hidden_initial_changed_queries_efficiently(self):
+        class WriterForm(forms.Form):
+            persons = forms.ModelMultipleChoiceField(
+                show_hidden_initial=True, queryset=Writer.objects.all()
+            )
+
+        writers = (Writer.objects.create(name=str(x)) for x in range(0, 50))
+        writer_pks = tuple(x.pk for x in writers)
+        form = WriterForm(data={"initial-persons": writer_pks})
+        with self.assertNumQueries(1):
+            self.assertTrue(form.has_changed())
+
+    def test_clean_does_deduplicate_values(self):
+        class PersonForm(forms.Form):
+            persons = forms.ModelMultipleChoiceField(queryset=Person.objects.all())
+
+        person1 = Person.objects.create(name="Person 1")
+        form = PersonForm(data={})
+        queryset = form.fields["persons"].clean([str(person1.pk)] * 50)
+        sql, params = queryset.query.sql_with_params()
+        self.assertEqual(len(params), 1)
+
+    def test_to_field_name_with_initial_data(self):
+        class ArticleCategoriesForm(forms.ModelForm):
+            categories = forms.ModelMultipleChoiceField(
+                Category.objects.all(), to_field_name="slug"
+            )
+
+            class Meta:
+                model = Article
+                fields = ["categories"]
+
+        article = Article.objects.create(
+            headline="Test article",
+            slug="test-article",
+            pub_date=datetime.date(1988, 1, 4),
+            writer=Writer.objects.create(name="Test writer"),
+            article="Hello.",
+        )
+        article.categories.add(self.c2, self.c3)
+        form = ArticleCategoriesForm(instance=article)
+        self.assertCountEqual(form["categories"].value(), [self.c2.slug, self.c3.slug])
+
+
+class ModelOneToOneFieldTests(TestCase):
+    def test_modelform_onetoonefield(self):
+        class ImprovedArticleForm(forms.ModelForm):
+            class Meta:
+                model = ImprovedArticle
+                fields = "__all__"
+
+        class ImprovedArticleWithParentLinkForm(forms.ModelForm):
+            class Meta:
+                model = ImprovedArticleWithParentLink
+                fields = "__all__"
+
+        self.assertEqual(list(ImprovedArticleForm.base_fields), ["article"])
+        self.assertEqual(list(ImprovedArticleWithParentLinkForm.base_fields), [])
+
+    def test_modelform_subclassed_model(self):
+        class BetterWriterForm(forms.ModelForm):
+            class Meta:
+                # BetterWriter model is a subclass of Writer with an additional
+                # `score` field.
+                model = BetterWriter
+                fields = "__all__"
+
+        bw = BetterWriter.objects.create(name="Joe Better", score=10)
+        self.assertEqual(
+            sorted(model_to_dict(bw)), ["id", "name", "score", "writer_ptr"]
+        )
+        self.assertEqual(sorted(model_to_dict(bw, fields=[])), [])
+        self.assertEqual(
+            sorted(model_to_dict(bw, fields=["id", "name"])), ["id", "name"]
+        )
+        self.assertEqual(
+            sorted(model_to_dict(bw, exclude=[])), ["id", "name", "score", "writer_ptr"]
+        )
+        self.assertEqual(
+            sorted(model_to_dict(bw, exclude=["id", "name"])), ["score", "writer_ptr"]
+        )
+
+        form = BetterWriterForm({"name": "Some Name", "score": 12})
+        self.assertTrue(form.is_valid())
+        bw2 = form.save()
+        self.assertEqual(bw2.score, 12)
+
+    def test_onetoonefield(self):
+        class WriterProfileForm(forms.ModelForm):
+            class Meta:
+                # WriterProfile has a OneToOneField to Writer
+                model = WriterProfile
+                fields = "__all__"
+
+        self.w_royko = Writer.objects.create(name="Mike Royko")
+        self.w_woodward = Writer.objects.create(name="Bob Woodward")
+
+        form = WriterProfileForm()
+        self.assertHTMLEqual(
+            form.as_p(),
+            """
+            <p><label for="id_writer">Writer:</label>
+            <select name="writer" id="id_writer" required>
+            <option value="" selected>---------</option>
+            <option value="%s">Bob Woodward</option>
+            <option value="%s">Mike Royko</option>
+            </select></p>
+            <p><label for="id_age">Age:</label>
+            <input type="number" name="age" id="id_age" min="0" required></p>
+            """
+            % (
+                self.w_woodward.pk,
+                self.w_royko.pk,
+            ),
+        )
+
+        data = {
+            "writer": str(self.w_woodward.pk),
+            "age": "65",
+        }
+        form = WriterProfileForm(data)
+        instance = form.save()
+        self.assertEqual(str(instance), "Bob Woodward is 65")
+
+        form = WriterProfileForm(instance=instance)
+        self.assertHTMLEqual(
+            form.as_p(),
+            """
+            <p><label for="id_writer">Writer:</label>
+            <select name="writer" id="id_writer" required>
+            <option value="">---------</option>
+            <option value="%s" selected>Bob Woodward</option>
+            <option value="%s">Mike Royko</option>
+            </select></p>
+            <p><label for="id_age">Age:</label>
+            <input type="number" name="age" value="65" id="id_age" min="0" required>
+            </p>"""
+            % (
+                self.w_woodward.pk,
+                self.w_royko.pk,
+            ),
+        )
+
+    def test_assignment_of_none(self):
+        class AuthorForm(forms.ModelForm):
+            class Meta:
+                model = Author
+                fields = ["publication", "full_name"]
+
+        publication = Publication.objects.create(
+            title="Pravda", date_published=datetime.date(1991, 8, 22)
+        )
+        author = Author.objects.create(publication=publication, full_name="John Doe")
+        form = AuthorForm({"publication": "", "full_name": "John Doe"}, instance=author)
+        self.assertTrue(form.is_valid())
+        self.assertIsNone(form.cleaned_data["publication"])
+        author = form.save()
+        # author object returned from form still retains original publication object
+        # that's why we need to retrieve it from database again
+        new_author = Author.objects.get(pk=author.pk)
+        self.assertIsNone(new_author.publication)
+
+    def test_assignment_of_none_null_false(self):
+        class AuthorForm(forms.ModelForm):
+            class Meta:
+                model = Author1
+                fields = ["publication", "full_name"]
+
+        publication = Publication.objects.create(
+            title="Pravda", date_published=datetime.date(1991, 8, 22)
+        )
+        author = Author1.objects.create(publication=publication, full_name="John Doe")
+        form = AuthorForm({"publication": "", "full_name": "John Doe"}, instance=author)
+        self.assertFalse(form.is_valid())
+
+
+class FileAndImageFieldTests(TestCase):
+    def test_clean_false(self):
+        """
+        If the ``clean`` method on a non-required FileField receives False as
+        the data (meaning clear the field value), it returns False, regardless
+        of the value of ``initial``.
+        """
+        f = forms.FileField(required=False)
+        self.assertIs(f.clean(False), False)
+        self.assertIs(f.clean(False, "initial"), False)
+
+    def test_clean_false_required(self):
+        """
+        If the ``clean`` method on a required FileField receives False as the
+        data, it has the same effect as None: initial is returned if non-empty,
+        otherwise the validation catches the lack of a required value.
+        """
+        f = forms.FileField(required=True)
+        self.assertEqual(f.clean(False, "initial"), "initial")
+        with self.assertRaises(ValidationError):
+            f.clean(False)
+
+    def test_full_clear(self):
+        """
+        Integration happy-path test that a model FileField can actually be set
+        and cleared via a ModelForm.
+        """
+
+        class DocumentForm(forms.ModelForm):
+            class Meta:
+                model = Document
+                fields = "__all__"
+
+        form = DocumentForm()
+        self.assertIn('name="myfile"', str(form))
+        self.assertNotIn("myfile-clear", str(form))
+        form = DocumentForm(
+            files={"myfile": SimpleUploadedFile("something.txt", b"content")}
+        )
+        self.assertTrue(form.is_valid())
+        doc = form.save(commit=False)
+        self.assertEqual(doc.myfile.name, "something.txt")
+        form = DocumentForm(instance=doc)
+        self.assertIn("myfile-clear", str(form))
+        form = DocumentForm(instance=doc, data={"myfile-clear": "true"})
+        doc = form.save(commit=False)
+        self.assertFalse(doc.myfile)
+
+    def test_clear_and_file_contradiction(self):
+        """
+        If the user submits a new file upload AND checks the clear checkbox,
+        they get a validation error, and the bound redisplay of the form still
+        includes the current file and the clear checkbox.
+        """
+
+        class DocumentForm(forms.ModelForm):
+            class Meta:
+                model = Document
+                fields = "__all__"
+
+        form = DocumentForm(
+            files={"myfile": SimpleUploadedFile("something.txt", b"content")}
+        )
+        self.assertTrue(form.is_valid())
+        doc = form.save(commit=False)
+        form = DocumentForm(
+            instance=doc,
+            files={"myfile": SimpleUploadedFile("something.txt", b"content")},
+            data={"myfile-clear": "true"},
+        )
+        self.assertTrue(not form.is_valid())
+        self.assertEqual(
+            form.errors["myfile"],
+            ["Please either submit a file or check the clear checkbox, not both."],
+        )
+        rendered = str(form)
+        self.assertIn("something.txt", rendered)
+        self.assertIn("myfile-clear", rendered)
+
+    def test_render_empty_file_field(self):
+        class DocumentForm(forms.ModelForm):
+            class Meta:
+                model = Document
+                fields = "__all__"
+
+        doc = Document.objects.create()
+        form = DocumentForm(instance=doc)
+        self.assertHTMLEqual(
+            str(form["myfile"]), '<input id="id_myfile" name="myfile" type="file">'
+        )
+
+    def test_file_field_data(self):
+        # Test conditions when files is either not given or empty.
+        f = TextFileForm(data={"description": "Assistance"})
+        self.assertFalse(f.is_valid())
+        f = TextFileForm(data={"description": "Assistance"}, files={})
+        self.assertFalse(f.is_valid())
+
+        # Upload a file and ensure it all works as expected.
+        f = TextFileForm(
+            data={"description": "Assistance"},
+            files={"file": SimpleUploadedFile("test1.txt", b"hello world")},
+        )
+        self.assertTrue(f.is_valid())
+        self.assertEqual(type(f.cleaned_data["file"]), SimpleUploadedFile)
+        instance = f.save()
+        self.assertEqual(instance.file.name, "tests/test1.txt")
+        instance.file.delete()
+
+        # If the previous file has been deleted, the file name can be reused
+        f = TextFileForm(
+            data={"description": "Assistance"},
+            files={"file": SimpleUploadedFile("test1.txt", b"hello world")},
+        )
+        self.assertTrue(f.is_valid())
+        self.assertEqual(type(f.cleaned_data["file"]), SimpleUploadedFile)
+        instance = f.save()
+        self.assertEqual(instance.file.name, "tests/test1.txt")
+
+        # Check if the max_length attribute has been inherited from the model.
+        f = TextFileForm(
+            data={"description": "Assistance"},
+            files={"file": SimpleUploadedFile("test-maxlength.txt", b"hello world")},
+        )
+        self.assertFalse(f.is_valid())
+
+        # Edit an instance that already has the file defined in the model. This will not
+        # save the file again, but leave it exactly as it is.
+        f = TextFileForm({"description": "Assistance"}, instance=instance)
+        self.assertTrue(f.is_valid())
+        self.assertEqual(f.cleaned_data["file"].name, "tests/test1.txt")
+        instance = f.save()
+        self.assertEqual(instance.file.name, "tests/test1.txt")
+
+        # Delete the current file since this is not done by Django.
+        instance.file.delete()
+
+        # Override the file by uploading a new one.
+        f = TextFileForm(
+            data={"description": "Assistance"},
+            files={"file": SimpleUploadedFile("test2.txt", b"hello world")},
+            instance=instance,
+        )
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.file.name, "tests/test2.txt")
+
+        # Delete the current file since this is not done by Django.
+        instance.file.delete()
+        instance.delete()
+
+    def test_filefield_required_false(self):
+        # Test the non-required FileField
+        f = TextFileForm(data={"description": "Assistance"})
+        f.fields["file"].required = False
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.file.name, "")
+
+        f = TextFileForm(
+            data={"description": "Assistance"},
+            files={"file": SimpleUploadedFile("test3.txt", b"hello world")},
+            instance=instance,
+        )
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.file.name, "tests/test3.txt")
+
+        # Instance can be edited w/out re-uploading the file and existing file
+        # should be preserved.
+        f = TextFileForm({"description": "New Description"}, instance=instance)
+        f.fields["file"].required = False
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.description, "New Description")
+        self.assertEqual(instance.file.name, "tests/test3.txt")
+
+        # Delete the current file since this is not done by Django.
+        instance.file.delete()
+        instance.delete()
+
+    def test_custom_file_field_save(self):
+        """
+        Regression for #11149: save_form_data should be called only once
+        """
+
+        class CFFForm(forms.ModelForm):
+            class Meta:
+                model = CustomFF
+                fields = "__all__"
+
+        # It's enough that the form saves without error -- the custom save routine will
+        # generate an AssertionError if it is called more than once during save.
+        form = CFFForm(data={"f": None})
+        form.save()
+
+    def test_file_field_multiple_save(self):
+        """
+        Simulate a file upload and check how many times Model.save() gets
+        called. Test for bug #639.
+        """
+
+        class PhotoForm(forms.ModelForm):
+            class Meta:
+                model = Photo
+                fields = "__all__"
+
+        # Grab an image for testing.
+        filename = os.path.join(os.path.dirname(__file__), "test.png")
+        with open(filename, "rb") as fp:
+            img = fp.read()
+
+        # Fake a POST QueryDict and FILES MultiValueDict.
+        data = {"title": "Testing"}
+        files = {"image": SimpleUploadedFile("test.png", img, "image/png")}
+
+        form = PhotoForm(data=data, files=files)
+        p = form.save()
+
+        try:
+            # Check the savecount stored on the object (see the model).
+            self.assertEqual(p._savecount, 1)
+        finally:
+            # Delete the "uploaded" file to avoid clogging /tmp.
+            p = Photo.objects.get()
+            p.image.delete(save=False)
+
+    def test_file_path_field_blank(self):
+        """FilePathField(blank=True) includes the empty option."""
+
+        class FPForm(forms.ModelForm):
+            class Meta:
+                model = FilePathModel
+                fields = "__all__"
+
+        form = FPForm()
+        self.assertEqual(
+            [name for _, name in form["path"].field.choices], ["---------", "models.py"]
+        )
+
+    @skipUnless(test_images, "Pillow not installed")
+    def test_image_field(self):
+        # ImageField and FileField are nearly identical, but they differ slightly when
+        # it comes to validation. This specifically tests that #6302 is fixed for
+        # both file fields and image fields.
+
+        with open(os.path.join(os.path.dirname(__file__), "test.png"), "rb") as fp:
+            image_data = fp.read()
+        with open(os.path.join(os.path.dirname(__file__), "test2.png"), "rb") as fp:
+            image_data2 = fp.read()
+
+        f = ImageFileForm(
+            data={"description": "An image"},
+            files={"image": SimpleUploadedFile("test.png", image_data)},
+        )
+        self.assertTrue(f.is_valid())
+        self.assertEqual(type(f.cleaned_data["image"]), SimpleUploadedFile)
+        instance = f.save()
+        self.assertEqual(instance.image.name, "tests/test.png")
+        self.assertEqual(instance.width, 16)
+        self.assertEqual(instance.height, 16)
+
+        # Delete the current file since this is not done by Django, but don't save
+        # because the dimension fields are not null=True.
+        instance.image.delete(save=False)
+        f = ImageFileForm(
+            data={"description": "An image"},
+            files={"image": SimpleUploadedFile("test.png", image_data)},
+        )
+        self.assertTrue(f.is_valid())
+        self.assertEqual(type(f.cleaned_data["image"]), SimpleUploadedFile)
+        instance = f.save()
+        self.assertEqual(instance.image.name, "tests/test.png")
+        self.assertEqual(instance.width, 16)
+        self.assertEqual(instance.height, 16)
+
+        # Edit an instance that already has the (required) image defined in the
+        # model. This will not save the image again, but leave it exactly as it
+        # is.
+
+        f = ImageFileForm(data={"description": "Look, it changed"}, instance=instance)
+        self.assertTrue(f.is_valid())
+        self.assertEqual(f.cleaned_data["image"].name, "tests/test.png")
+        instance = f.save()
+        self.assertEqual(instance.image.name, "tests/test.png")
+        self.assertEqual(instance.height, 16)
+        self.assertEqual(instance.width, 16)
+
+        # Delete the current file since this is not done by Django, but don't save
+        # because the dimension fields are not null=True.
+        instance.image.delete(save=False)
+        # Override the file by uploading a new one.
+
+        f = ImageFileForm(
+            data={"description": "Changed it"},
+            files={"image": SimpleUploadedFile("test2.png", image_data2)},
+            instance=instance,
+        )
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.image.name, "tests/test2.png")
+        self.assertEqual(instance.height, 32)
+        self.assertEqual(instance.width, 48)
+
+        # Delete the current file since this is not done by Django, but don't save
+        # because the dimension fields are not null=True.
+        instance.image.delete(save=False)
+        instance.delete()
+
+        f = ImageFileForm(
+            data={"description": "Changed it"},
+            files={"image": SimpleUploadedFile("test2.png", image_data2)},
+        )
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.image.name, "tests/test2.png")
+        self.assertEqual(instance.height, 32)
+        self.assertEqual(instance.width, 48)
+
+        # Delete the current file since this is not done by Django, but don't save
+        # because the dimension fields are not null=True.
+        instance.image.delete(save=False)
+        instance.delete()
+
+        # Test the non-required ImageField
+        # Note: In Oracle, we expect a null ImageField to return '' instead of
+        # None.
+        if connection.features.interprets_empty_strings_as_nulls:
+            expected_null_imagefield_repr = ""
+        else:
+            expected_null_imagefield_repr = None
+
+        f = OptionalImageFileForm(data={"description": "Test"})
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.image.name, expected_null_imagefield_repr)
+        self.assertIsNone(instance.width)
+        self.assertIsNone(instance.height)
+
+        f = OptionalImageFileForm(
+            data={"description": "And a final one"},
+            files={"image": SimpleUploadedFile("test3.png", image_data)},
+            instance=instance,
+        )
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.image.name, "tests/test3.png")
+        self.assertEqual(instance.width, 16)
+        self.assertEqual(instance.height, 16)
+
+        # Editing the instance without re-uploading the image should not affect
+        # the image or its width/height properties.
+        f = OptionalImageFileForm({"description": "New Description"}, instance=instance)
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.description, "New Description")
+        self.assertEqual(instance.image.name, "tests/test3.png")
+        self.assertEqual(instance.width, 16)
+        self.assertEqual(instance.height, 16)
+
+        # Delete the current file since this is not done by Django.
+        instance.image.delete()
+        instance.delete()
+
+        f = OptionalImageFileForm(
+            data={"description": "And a final one"},
+            files={"image": SimpleUploadedFile("test4.png", image_data2)},
+        )
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.image.name, "tests/test4.png")
+        self.assertEqual(instance.width, 48)
+        self.assertEqual(instance.height, 32)
+        instance.delete()
+        # Callable upload_to behavior that's dependent on the value of another
+        # field in the model.
+        f = ImageFileForm(
+            data={"description": "And a final one", "path": "foo"},
+            files={"image": SimpleUploadedFile("test4.png", image_data)},
+        )
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.image.name, "foo/test4.png")
+        instance.delete()
+
+        # Editing an instance that has an image without an extension shouldn't
+        # fail validation. First create:
+        f = NoExtensionImageFileForm(
+            data={"description": "An image"},
+            files={"image": SimpleUploadedFile("test.png", image_data)},
+        )
+        self.assertTrue(f.is_valid())
+        instance = f.save()
+        self.assertEqual(instance.image.name, "tests/no_extension")
+        # Then edit:
+        f = NoExtensionImageFileForm(
+            data={"description": "Edited image"}, instance=instance
+        )
+        self.assertTrue(f.is_valid())
+
+
+class ModelOtherFieldTests(SimpleTestCase):
+    def test_big_integer_field(self):
+        bif = BigIntForm({"biggie": "-9223372036854775808"})
+        self.assertTrue(bif.is_valid())
+        bif = BigIntForm({"biggie": "-9223372036854775809"})
+        self.assertFalse(bif.is_valid())
+        self.assertEqual(
+            bif.errors,
+            {
+                "biggie": [
+                    "Ensure this value is greater than or equal to "
+                    "-9223372036854775808."
+                ]
+            },
+        )
+        bif = BigIntForm({"biggie": "9223372036854775807"})
+        self.assertTrue(bif.is_valid())
+        bif = BigIntForm({"biggie": "9223372036854775808"})
+        self.assertFalse(bif.is_valid())
+        self.assertEqual(
+            bif.errors,
+            {
+                "biggie": [
+                    "Ensure this value is less than or equal to 9223372036854775807."
+                ]
+            },
+        )
+
+    @ignore_warnings(category=RemovedInDjango60Warning)
+    def test_url_on_modelform(self):
+        "Check basic URL field validation on model forms"
+
+        class HomepageForm(forms.ModelForm):
+            class Meta:
+                model = Homepage
+                fields = "__all__"
+
+        self.assertFalse(HomepageForm({"url": "foo"}).is_valid())
+        self.assertFalse(HomepageForm({"url": "http://"}).is_valid())
+        self.assertFalse(HomepageForm({"url": "http://example"}).is_valid())
+        self.assertFalse(HomepageForm({"url": "http://example."}).is_valid())
+        self.assertFalse(HomepageForm({"url": "http://com."}).is_valid())
+
+        self.assertTrue(HomepageForm({"url": "http://localhost"}).is_valid())
+        self.assertTrue(HomepageForm({"url": "http://example.com"}).is_valid())
+        self.assertTrue(HomepageForm({"url": "http://www.example.com"}).is_valid())
+        self.assertTrue(HomepageForm({"url": "http://www.example.com:8000"}).is_valid())
+        self.assertTrue(HomepageForm({"url": "http://www.example.com/test"}).is_valid())
+        self.assertTrue(
+            HomepageForm({"url": "http://www.example.com:8000/test"}).is_valid()
+        )
+        self.assertTrue(HomepageForm({"url": "http://example.com/foo/bar"}).is_valid())
+
+    def test_url_modelform_assume_scheme_warning(self):
+        msg = (
+            "The default scheme will be changed from 'http' to 'https' in Django "
+            "6.0. Pass the forms.URLField.assume_scheme argument to silence this "
+            "warning."
+        )
+        with self.assertWarnsMessage(RemovedInDjango60Warning, msg):
+
+            class HomepageForm(forms.ModelForm):
+                class Meta:
+                    model = Homepage
+                    fields = "__all__"
+
+    def test_modelform_non_editable_field(self):
+        """
+        When explicitly including a non-editable field in a ModelForm, the
+        error message should be explicit.
+        """
+        # 'created', non-editable, is excluded by default
+        self.assertNotIn("created", ArticleForm().fields)
+
+        msg = (
+            "'created' cannot be specified for Article model form as it is a "
+            "non-editable field"
+        )
+        with self.assertRaisesMessage(FieldError, msg):
+
+            class InvalidArticleForm(forms.ModelForm):
+                class Meta:
+                    model = Article
+                    fields = ("headline", "created")
+
+    def test_https_prefixing(self):
+        """
+        If the https:// prefix is omitted on form input, the field adds it
+        again.
+        """
+
+        class HomepageForm(forms.ModelForm):
+            # RemovedInDjango60Warning.
+            url = forms.URLField(assume_scheme="https")
+
+            class Meta:
+                model = Homepage
+                fields = "__all__"
+
+        form = HomepageForm({"url": "example.com"})
+        self.assertTrue(form.is_valid())
+        self.assertEqual(form.cleaned_data["url"], "https://example.com")
+
+        form = HomepageForm({"url": "example.com/test"})
+        self.assertTrue(form.is_valid())
+        self.assertEqual(form.cleaned_data["url"], "https://example.com/test")
+
+
+class OtherModelFormTests(TestCase):
+    def test_media_on_modelform(self):
+        # Similar to a regular Form class you can define custom media to be used on
+        # the ModelForm.
+        f = ModelFormWithMedia()
+        self.assertHTMLEqual(
+            str(f.media),
+            '<link href="/some/form/css" media="all" rel="stylesheet">'
+            '<script src="/some/form/javascript"></script>',
+        )
+
+    def test_choices_type(self):
+        # Choices on CharField and IntegerField
+        f = ArticleForm()
+        with self.assertRaises(ValidationError):
+            f.fields["status"].clean("42")
+
+        f = ArticleStatusForm()
+        with self.assertRaises(ValidationError):
+            f.fields["status"].clean("z")
+
+    def test_prefetch_related_queryset(self):
+        """
+        ModelChoiceField should respect a prefetch_related() on its queryset.
+        """
+        blue = Colour.objects.create(name="blue")
+        red = Colour.objects.create(name="red")
+        multicolor_item = ColourfulItem.objects.create()
+        multicolor_item.colours.add(blue, red)
+        red_item = ColourfulItem.objects.create()
+        red_item.colours.add(red)
+
+        class ColorModelChoiceField(forms.ModelChoiceField):
+            def label_from_instance(self, obj):
+                return ", ".join(c.name for c in obj.colours.all())
+
+        field = ColorModelChoiceField(ColourfulItem.objects.prefetch_related("colours"))
+        with self.assertNumQueries(3):  # would be 4 if prefetch is ignored
+            self.assertEqual(
+                tuple(field.choices),
+                (
+                    ("", "---------"),
+                    (multicolor_item.pk, "blue, red"),
+                    (red_item.pk, "red"),
+                ),
+            )
+
+    def test_foreignkeys_which_use_to_field(self):
+        apple = Inventory.objects.create(barcode=86, name="Apple")
+        pear = Inventory.objects.create(barcode=22, name="Pear")
+        core = Inventory.objects.create(barcode=87, name="Core", parent=apple)
+
+        field = forms.ModelChoiceField(Inventory.objects.all(), to_field_name="barcode")
+        self.assertEqual(
+            tuple(field.choices),
+            (("", "---------"), (86, "Apple"), (87, "Core"), (22, "Pear")),
+        )
+
+        form = InventoryForm(instance=core)
+        self.assertHTMLEqual(
+            str(form["parent"]),
+            """<select name="parent" id="id_parent">
+<option value="">---------</option>
+<option value="86" selected>Apple</option>
+<option value="87">Core</option>
+<option value="22">Pear</option>
+</select>""",
+        )
+        data = model_to_dict(core)
+        data["parent"] = "22"
+        form = InventoryForm(data=data, instance=core)
+        core = form.save()
+        self.assertEqual(core.parent.name, "Pear")
+
+        class CategoryForm(forms.ModelForm):
+            description = forms.CharField()
+
+            class Meta:
+                model = Category
+                fields = ["description", "url"]
+
+        self.assertEqual(list(CategoryForm.base_fields), ["description", "url"])
+
+        self.assertHTMLEqual(
+            str(CategoryForm()),
+            '<div><label for="id_description">Description:</label><input type="text" '
+            'name="description" required id="id_description"></div><div>'
+            '<label for="id_url">The URL:</label><input type="text" name="url" '
+            'maxlength="40" required id="id_url"></div>',
+        )
+        # to_field_name should also work on ModelMultipleChoiceField ##################
+
+        field = forms.ModelMultipleChoiceField(
+            Inventory.objects.all(), to_field_name="barcode"
+        )
+        self.assertEqual(
+            tuple(field.choices), ((86, "Apple"), (87, "Core"), (22, "Pear"))
+        )
+        self.assertSequenceEqual(field.clean([86]), [apple])
+
+        form = SelectInventoryForm({"items": [87, 22]})
+        self.assertTrue(form.is_valid())
+        self.assertEqual(len(form.cleaned_data), 1)
+        self.assertSequenceEqual(form.cleaned_data["items"], [core, pear])
+
+    def test_model_field_that_returns_none_to_exclude_itself_with_explicit_fields(self):
+        self.assertEqual(list(CustomFieldForExclusionForm.base_fields), ["name"])
+        self.assertHTMLEqual(
+            str(CustomFieldForExclusionForm()),
+            '<div><label for="id_name">Name:</label><input type="text" '
+            'name="name" maxlength="10" required id="id_name"></div>',
+        )
+
+    def test_iterable_model_m2m(self):
+        class ColourfulItemForm(forms.ModelForm):
+            class Meta:
+                model = ColourfulItem
+                fields = "__all__"
+
+        colour = Colour.objects.create(name="Blue")
+        form = ColourfulItemForm()
+        self.maxDiff = 1024
+        self.assertHTMLEqual(
+            form.as_p(),
+            """
+            <p>
+            <label for="id_name">Name:</label>
+            <input id="id_name" type="text" name="name" maxlength="50" required></p>
+            <p><label for="id_colours">Colours:</label>
+            <select multiple name="colours" id="id_colours" required>
+            <option value="%(blue_pk)s">Blue</option>
+            </select></p>
+            """
+            % {"blue_pk": colour.pk},
+        )
+
+    def test_callable_field_default(self):
+        class PublicationDefaultsForm(forms.ModelForm):
+            class Meta:
+                model = PublicationDefaults
+                fields = ("title", "date_published", "mode", "category")
+
+        self.maxDiff = 2000
+        form = PublicationDefaultsForm()
+        today_str = str(datetime.date.today())
+        self.assertHTMLEqual(
+            form.as_p(),
+            """
+            <p><label for="id_title">Title:</label>
+            <input id="id_title" maxlength="30" name="title" type="text" required>
+            </p>
+            <p><label for="id_date_published">Date published:</label>
+            <input id="id_date_published" name="date_published" type="text" value="{0}"
+                required>
+            <input id="initial-id_date_published" name="initial-date_published"
+                type="hidden" value="{0}">
+            </p>
+            <p><label for="id_mode">Mode:</label> <select id="id_mode" name="mode">
+            <option value="di" selected>direct</option>
+            <option value="de">delayed</option></select>
+            <input id="initial-id_mode" name="initial-mode" type="hidden" value="di">
+            </p>
+            <p>
+            <label for="id_category">Category:</label>
+            <select id="id_category" name="category">
+            <option value="1">Games</option>
+            <option value="2">Comics</option>
+            <option value="3" selected>Novel</option></select>
+            <input id="initial-id_category" name="initial-category" type="hidden"
+                value="3">
+            """.format(
+                today_str
+            ),
+        )
+        empty_data = {
+            "title": "",
+            "date_published": today_str,
+            "initial-date_published": today_str,
+            "mode": "di",
+            "initial-mode": "di",
+            "category": "3",
+            "initial-category": "3",
+        }
+        bound_form = PublicationDefaultsForm(empty_data)
+        self.assertFalse(bound_form.has_changed())
+
+
+class ModelFormCustomErrorTests(SimpleTestCase):
+    def test_custom_error_messages(self):
+        data = {"name1": "@#$!!**@#$", "name2": "@#$!!**@#$"}
+        errors = CustomErrorMessageForm(data).errors
+        self.assertHTMLEqual(
+            str(errors["name1"]),
+            '<ul class="errorlist"><li>Form custom error message.</li></ul>',
+        )
+        self.assertHTMLEqual(
+            str(errors["name2"]),
+            '<ul class="errorlist"><li>Model custom error message.</li></ul>',
+        )
+
+    def test_model_clean_error_messages(self):
+        data = {"name1": "FORBIDDEN_VALUE", "name2": "ABC"}
+        form = CustomErrorMessageForm(data)
+        self.assertFalse(form.is_valid())
+        self.assertHTMLEqual(
+            str(form.errors["name1"]),
+            '<ul class="errorlist"><li>Model.clean() error messages.</li></ul>',
+        )
+        data = {"name1": "FORBIDDEN_VALUE2", "name2": "ABC"}
+        form = CustomErrorMessageForm(data)
+        self.assertFalse(form.is_valid())
+        self.assertHTMLEqual(
+            str(form.errors["name1"]),
+            '<ul class="errorlist">'
+            "<li>Model.clean() error messages (simpler syntax).</li></ul>",
+        )
+        data = {"name1": "GLOBAL_ERROR", "name2": "ABC"}
+        form = CustomErrorMessageForm(data)
+        self.assertFalse(form.is_valid())
+        self.assertEqual(form.errors["__all__"], ["Global error message."])
+
+
+class CustomCleanTests(TestCase):
+    def test_override_clean(self):
+        """
+        Regression for #12596: Calling super from ModelForm.clean() should be
+        optional.
+        """
+
+        class TripleFormWithCleanOverride(forms.ModelForm):
+            class Meta:
+                model = Triple
+                fields = "__all__"
+
+            def clean(self):
+                if not self.cleaned_data["left"] == self.cleaned_data["right"]:
+                    raise ValidationError("Left and right should be equal")
+                return self.cleaned_data
+
+        form = TripleFormWithCleanOverride({"left": 1, "middle": 2, "right": 1})
+        self.assertTrue(form.is_valid())
+        # form.instance.left will be None if the instance was not constructed
+        # by form.full_clean().
+        self.assertEqual(form.instance.left, 1)
+
+    def test_model_form_clean_applies_to_model(self):
+        """
+        Regression test for #12960. Make sure the cleaned_data returned from
+        ModelForm.clean() is applied to the model instance.
+        """
+
+        class CategoryForm(forms.ModelForm):
+            class Meta:
+                model = Category
+                fields = "__all__"
+
+            def clean(self):
+                self.cleaned_data["name"] = self.cleaned_data["name"].upper()
+                return self.cleaned_data
+
+        data = {"name": "Test", "slug": "test", "url": "/test"}
+        form = CategoryForm(data)
+        category = form.save()
+        self.assertEqual(category.name, "TEST")
+
+
+class ModelFormInheritanceTests(SimpleTestCase):
+    def test_form_subclass_inheritance(self):
+        class Form(forms.Form):
+            age = forms.IntegerField()
+
+        class ModelForm(forms.ModelForm, Form):
+            class Meta:
+                model = Writer
+                fields = "__all__"
+
+        self.assertEqual(list(ModelForm().fields), ["name", "age"])
+
+    def test_field_removal(self):
+        class ModelForm(forms.ModelForm):
+            class Meta:
+                model = Writer
+                fields = "__all__"
+
+        class Mixin:
+            age = None
+
+        class Form(forms.Form):
+            age = forms.IntegerField()
+
+        class Form2(forms.Form):
+            foo = forms.IntegerField()
+
+        self.assertEqual(list(ModelForm().fields), ["name"])
+        self.assertEqual(list(type("NewForm", (Mixin, Form), {})().fields), [])
+        self.assertEqual(
+            list(type("NewForm", (Form2, Mixin, Form), {})().fields), ["foo"]
+        )
+        self.assertEqual(
+            list(type("NewForm", (Mixin, ModelForm, Form), {})().fields), ["name"]
+        )
+        self.assertEqual(
+            list(type("NewForm", (ModelForm, Mixin, Form), {})().fields), ["name"]
+        )
+        self.assertEqual(
+            list(type("NewForm", (ModelForm, Form, Mixin), {})().fields),
+            ["name", "age"],
+        )
+        self.assertEqual(
+            list(type("NewForm", (ModelForm, Form), {"age": None})().fields), ["name"]
+        )
+
+    def test_field_removal_name_clashes(self):
+        """
+        Form fields can be removed in subclasses by setting them to None
+        (#22510).
+        """
+
+        class MyForm(forms.ModelForm):
+            media = forms.CharField()
+
+            class Meta:
+                model = Writer
+                fields = "__all__"
+
+        class SubForm(MyForm):
+            media = None
+
+        self.assertIn("media", MyForm().fields)
+        self.assertNotIn("media", SubForm().fields)
+        self.assertTrue(hasattr(MyForm, "media"))
+        self.assertTrue(hasattr(SubForm, "media"))
+
+
+class StumpJokeForm(forms.ModelForm):
+    class Meta:
+        model = StumpJoke
+        fields = "__all__"
+
+
+class CustomFieldWithQuerysetButNoLimitChoicesTo(forms.Field):
+    queryset = 42
+
+
+class StumpJokeWithCustomFieldForm(forms.ModelForm):
+    custom = CustomFieldWithQuerysetButNoLimitChoicesTo()
+
+    class Meta:
+        model = StumpJoke
+        fields = ()
+
+
+class LimitChoicesToTests(TestCase):
+    """
+    Tests the functionality of ``limit_choices_to``.
+    """
+
+    @classmethod
+    def setUpTestData(cls):
+        cls.threepwood = Character.objects.create(
+            username="threepwood",
+            last_action=datetime.datetime.today() + datetime.timedelta(days=1),
+        )
+        cls.marley = Character.objects.create(
+            username="marley",
+            last_action=datetime.datetime.today() - datetime.timedelta(days=1),
+        )
+
+    def test_limit_choices_to_callable_for_fk_rel(self):
+        """
+        A ForeignKey can use limit_choices_to as a callable (#2554).
+        """
+        stumpjokeform = StumpJokeForm()
+        self.assertSequenceEqual(
+            stumpjokeform.fields["most_recently_fooled"].queryset, [self.threepwood]
+        )
+
+    def test_limit_choices_to_callable_for_m2m_rel(self):
+        """
+        A ManyToManyField can use limit_choices_to as a callable (#2554).
+        """
+        stumpjokeform = StumpJokeForm()
+        self.assertSequenceEqual(
+            stumpjokeform.fields["most_recently_fooled"].queryset, [self.threepwood]
+        )
+
+    def test_custom_field_with_queryset_but_no_limit_choices_to(self):
+        """
+        A custom field with a `queryset` attribute but no `limit_choices_to`
+        works (#23795).
+        """
+        f = StumpJokeWithCustomFieldForm()
+        self.assertEqual(f.fields["custom"].queryset, 42)
+
+    def test_fields_for_model_applies_limit_choices_to(self):
+        fields = fields_for_model(StumpJoke, ["has_fooled_today"])
+        self.assertSequenceEqual(fields["has_fooled_today"].queryset, [self.threepwood])
+
+    def test_callable_called_each_time_form_is_instantiated(self):
+        field = StumpJokeForm.base_fields["most_recently_fooled"]
+        with mock.patch.object(field, "limit_choices_to") as today_callable_dict:
+            StumpJokeForm()
+            self.assertEqual(today_callable_dict.call_count, 1)
+            StumpJokeForm()
+            self.assertEqual(today_callable_dict.call_count, 2)
+            StumpJokeForm()
+            self.assertEqual(today_callable_dict.call_count, 3)
+
+    @isolate_apps("model_forms")
+    def test_limit_choices_to_no_duplicates(self):
+        joke1 = StumpJoke.objects.create(
+            funny=True,
+            most_recently_fooled=self.threepwood,
+        )
+        joke2 = StumpJoke.objects.create(
+            funny=True,
+            most_recently_fooled=self.threepwood,
+        )
+        joke3 = StumpJoke.objects.create(
+            funny=True,
+            most_recently_fooled=self.marley,
+        )
+        StumpJoke.objects.create(funny=False, most_recently_fooled=self.marley)
+        joke1.has_fooled_today.add(self.marley, self.threepwood)
+        joke2.has_fooled_today.add(self.marley)
+        joke3.has_fooled_today.add(self.marley, self.threepwood)
+
+        class CharacterDetails(models.Model):
+            character1 = models.ForeignKey(
+                Character,
+                models.CASCADE,
+                limit_choices_to=models.Q(
+                    jokes__funny=True,
+                    jokes_today__funny=True,
+                ),
+                related_name="details_fk_1",
+            )
+            character2 = models.ForeignKey(
+                Character,
+                models.CASCADE,
+                limit_choices_to={
+                    "jokes__funny": True,
+                    "jokes_today__funny": True,
+                },
+                related_name="details_fk_2",
+            )
+            character3 = models.ManyToManyField(
+                Character,
+                limit_choices_to=models.Q(
+                    jokes__funny=True,
+                    jokes_today__funny=True,
+                ),
+                related_name="details_m2m_1",
+            )
+
+        class CharacterDetailsForm(forms.ModelForm):
+            class Meta:
+                model = CharacterDetails
+                fields = "__all__"
+
+        form = CharacterDetailsForm()
+        self.assertCountEqual(
+            form.fields["character1"].queryset,
+            [self.marley, self.threepwood],
+        )
+        self.assertCountEqual(
+            form.fields["character2"].queryset,
+            [self.marley, self.threepwood],
+        )
+        self.assertCountEqual(
+            form.fields["character3"].queryset,
+            [self.marley, self.threepwood],
+        )
+
+    def test_limit_choices_to_m2m_through(self):
+        class DiceForm(forms.ModelForm):
+            class Meta:
+                model = Dice
+                fields = ["numbers"]
+
+        Number.objects.create(value=0)
+        n1 = Number.objects.create(value=1)
+        n2 = Number.objects.create(value=2)
+
+        form = DiceForm()
+        self.assertCountEqual(form.fields["numbers"].queryset, [n1, n2])
+
+
+class FormFieldCallbackTests(SimpleTestCase):
+    def test_baseform_with_widgets_in_meta(self):
+        """
+        Using base forms with widgets defined in Meta should not raise errors.
+        """
+        widget = forms.Textarea()
+
+        class BaseForm(forms.ModelForm):
+            class Meta:
+                model = Person
+                widgets = {"name": widget}
+                fields = "__all__"
+
+        Form = modelform_factory(Person, form=BaseForm)
+        self.assertIsInstance(Form.base_fields["name"].widget, forms.Textarea)
+
+    def test_factory_with_widget_argument(self):
+        """Regression for #15315: modelform_factory should accept widgets
+        argument
+        """
+        widget = forms.Textarea()
+
+        # Without a widget should not set the widget to textarea
+        Form = modelform_factory(Person, fields="__all__")
+        self.assertNotEqual(Form.base_fields["name"].widget.__class__, forms.Textarea)
+
+        # With a widget should not set the widget to textarea
+        Form = modelform_factory(Person, fields="__all__", widgets={"name": widget})
+        self.assertEqual(Form.base_fields["name"].widget.__class__, forms.Textarea)
+
+    def test_modelform_factory_without_fields(self):
+        """Regression for #19733"""
+        message = (
+            "Calling modelform_factory without defining 'fields' or 'exclude' "
+            "explicitly is prohibited."
+        )
+        with self.assertRaisesMessage(ImproperlyConfigured, message):
+            modelform_factory(Person)
+
+    def test_modelform_factory_with_all_fields(self):
+        """Regression for #19733"""
+        form = modelform_factory(Person, fields="__all__")
+        self.assertEqual(list(form.base_fields), ["name"])
+
+    def test_custom_callback(self):
+        """A custom formfield_callback is used if provided"""
+        callback_args = []
+
+        def callback(db_field, **kwargs):
+            callback_args.append((db_field, kwargs))
+            return db_field.formfield(**kwargs)
+
+        widget = forms.Textarea()
+
+        class BaseForm(forms.ModelForm):
+            class Meta:
+                model = Person
+                widgets = {"name": widget}
+                fields = "__all__"
+
+        modelform_factory(Person, form=BaseForm, formfield_callback=callback)
+        id_field, name_field = Person._meta.fields
+
+        self.assertEqual(
+            callback_args, [(id_field, {}), (name_field, {"widget": widget})]
+        )
+
+    def test_bad_callback(self):
+        # A bad callback provided by user still gives an error
+        with self.assertRaises(TypeError):
+            modelform_factory(
+                Person,
+                fields="__all__",
+                formfield_callback="not a function or callable",
+            )
+
+    def test_inherit_after_custom_callback(self):
+        def callback(db_field, **kwargs):
+            if isinstance(db_field, models.CharField):
+                return forms.CharField(widget=forms.Textarea)
+            return db_field.formfield(**kwargs)
+
+        class BaseForm(forms.ModelForm):
+            class Meta:
+                model = Person
+                fields = "__all__"
+
+        NewForm = modelform_factory(Person, form=BaseForm, formfield_callback=callback)
+
+        class InheritedForm(NewForm):
+            pass
+
+        for name in NewForm.base_fields:
+            self.assertEqual(
+                type(InheritedForm.base_fields[name].widget),
+                type(NewForm.base_fields[name].widget),
+            )
+
+    def test_custom_callback_in_meta(self):
+        def callback(db_field, **kwargs):
+            return forms.CharField(widget=forms.Textarea)
+
+        class NewForm(forms.ModelForm):
+            class Meta:
+                model = Person
+                fields = ["id", "name"]
+                formfield_callback = callback
+
+        for field in NewForm.base_fields.values():
+            self.assertEqual(type(field.widget), forms.Textarea)
+
+    def test_custom_callback_from_base_form_meta(self):
+        def callback(db_field, **kwargs):
+            return forms.CharField(widget=forms.Textarea)
+
+        class BaseForm(forms.ModelForm):
+            class Meta:
+                model = Person
+                fields = "__all__"
+                formfield_callback = callback
+
+        NewForm = modelform_factory(model=Person, form=BaseForm)
+
+        class InheritedForm(NewForm):
+            pass
+
+        for name, field in NewForm.base_fields.items():
+            self.assertEqual(type(field.widget), forms.Textarea)
+            self.assertEqual(
+                type(field.widget),
+                type(InheritedForm.base_fields[name].widget),
+            )
+
+
+class LocalizedModelFormTest(TestCase):
+    def test_model_form_applies_localize_to_some_fields(self):
+        class PartiallyLocalizedTripleForm(forms.ModelForm):
+            class Meta:
+                model = Triple
+                localized_fields = (
+                    "left",
+                    "right",
+                )
+                fields = "__all__"
+
+        f = PartiallyLocalizedTripleForm({"left": 10, "middle": 10, "right": 10})
+        self.assertTrue(f.is_valid())
+        self.assertTrue(f.fields["left"].localize)
+        self.assertFalse(f.fields["middle"].localize)
+        self.assertTrue(f.fields["right"].localize)
+
+    def test_model_form_applies_localize_to_all_fields(self):
+        class FullyLocalizedTripleForm(forms.ModelForm):
+            class Meta:
+                model = Triple
+                localized_fields = "__all__"
+                fields = "__all__"
+
+        f = FullyLocalizedTripleForm({"left": 10, "middle": 10, "right": 10})
+        self.assertTrue(f.is_valid())
+        self.assertTrue(f.fields["left"].localize)
+        self.assertTrue(f.fields["middle"].localize)
+        self.assertTrue(f.fields["right"].localize)
+
+    def test_model_form_refuses_arbitrary_string(self):
+        msg = (
+            "BrokenLocalizedTripleForm.Meta.localized_fields "
+            "cannot be a string. Did you mean to type: ('foo',)?"
+        )
+        with self.assertRaisesMessage(TypeError, msg):
+
+            class BrokenLocalizedTripleForm(forms.ModelForm):
+                class Meta:
+                    model = Triple
+                    localized_fields = "foo"
+
+
+class CustomMetaclass(ModelFormMetaclass):
+    def __new__(cls, name, bases, attrs):
+        new = super().__new__(cls, name, bases, attrs)
+        new.base_fields = {}
+        return new
+
+
+class CustomMetaclassForm(forms.ModelForm, metaclass=CustomMetaclass):
+    pass
+
+
+class CustomMetaclassTestCase(SimpleTestCase):
+    def test_modelform_factory_metaclass(self):
+        new_cls = modelform_factory(Person, fields="__all__", form=CustomMetaclassForm)
+        self.assertEqual(new_cls.base_fields, {})
+
+
+class StrictAssignmentTests(SimpleTestCase):
+    """
+    Should a model do anything special with __setattr__() or descriptors which
+    raise a ValidationError, a model form should catch the error (#24706).
+    """
+
+    def test_setattr_raises_validation_error_field_specific(self):
+        """
+        A model ValidationError using the dict form should put the error
+        message into the correct key of form.errors.
+        """
+        form_class = modelform_factory(
+            model=StrictAssignmentFieldSpecific, fields=["title"]
+        )
+        form = form_class(data={"title": "testing setattr"}, files=None)
+        # This line turns on the ValidationError; it avoids the model erroring
+        # when its own __init__() is called when creating form.instance.
+        form.instance._should_error = True
+        self.assertFalse(form.is_valid())
+        self.assertEqual(
+            form.errors,
+            {"title": ["Cannot set attribute", "This field cannot be blank."]},
+        )
+
+    def test_setattr_raises_validation_error_non_field(self):
+        """
+        A model ValidationError not using the dict form should put the error
+        message into __all__ (i.e. non-field errors) on the form.
+        """
+        form_class = modelform_factory(model=StrictAssignmentAll, fields=["title"])
+        form = form_class(data={"title": "testing setattr"}, files=None)
+        # This line turns on the ValidationError; it avoids the model erroring
+        # when its own __init__() is called when creating form.instance.
+        form.instance._should_error = True
+        self.assertFalse(form.is_valid())
+        self.assertEqual(
+            form.errors,
+            {
+                "__all__": ["Cannot set attribute"],
+                "title": ["This field cannot be blank."],
+            },
+        )
+
+
+class ModelToDictTests(TestCase):
+    def test_many_to_many(self):
+        """Data for a ManyToManyField is a list rather than a lazy QuerySet."""
+        blue = Colour.objects.create(name="blue")
+        red = Colour.objects.create(name="red")
+        item = ColourfulItem.objects.create()
+        item.colours.set([blue])
+        data = model_to_dict(item)["colours"]
+        self.assertEqual(data, [blue])
+        item.colours.set([red])
+        # If data were a QuerySet, it would be reevaluated here and give "red"
+        # instead of the original value.
+        self.assertEqual(data, [blue])