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see the test package documentation.<topic_end>
<topic_start>
1. Add the test dependency
The test package provides the core functionality for
writing tests in Dart. This is the best approach when
writing packages consumed by web, server, and Flutter apps.To add the test package as a dev dependency,
run flutter pub add:<topic_end>
<topic_start>
2. Create a test file
In this example, create two files: counter.dart and counter_test.dart.The counter.dart file contains a class that you want to test and
resides in the lib folder. The counter_test.dart file contains
the tests themselves and lives inside the test folder.In general, test files should reside inside a test folder
located at the root of your Flutter application or package.
Test files should always end with _test.dart,
this is the convention used by the test runner when searching for tests.When you’re finished, the folder structure should look like this:<topic_end>
<topic_start>
3. Create a class to test
Next, you need a “unit” to test. Remember: “unit” is another name for a
function, method, or class. For this example, create a Counter class
inside the lib/counter.dart file. It is responsible for incrementing
and decrementing a value starting at 0.
<code_start>class Counter {
int value = 0;
void increment() => value++;
void decrement() => value--;
}<code_end>
Note: For simplicity, this tutorial does not follow the “Test Driven
Development” approach. If you’re more comfortable with that style of
development, you can always go that route.<topic_end>
<topic_start>
4. Write a test for our class
Inside the counter_test.dart file, write the first unit test. Tests are
defined using the top-level test function, and you can check if the results
are correct by using the top-level expect function.
Both of these functions come from the test package.
<code_start>// Import the test package and Counter class
import 'package:counter_app/counter.dart';
import 'package:test/test.dart';
void main() {
test('Counter value should be incremented', () {
final counter = Counter();
counter.increment();
expect(counter.value, 1);
});
}<code_end>
<topic_end>
<topic_start>
5. Combine multiple tests in a group
If you want to run a series of related tests,
use the flutter_test package group function to categorize the tests.
Once put into a group, you can call flutter test on all tests in
that group with one command.
<code_start>import 'package:counter_app/counter.dart';
import 'package:test/test.dart';
void main() {
group('Test start, increment, decrement', () {
test('value should start at 0', () {
expect(Counter().value, 0);
});
test('value should be incremented', () {
final counter = Counter();
counter.increment();
expect(counter.value, 1);
});
test('value should be decremented', () {
final counter = Counter();
counter.decrement();
expect(counter.value, -1);
});
});
}<code_end>
<topic_end>
<topic_start>
6. Run the tests
Now that you have a Counter class with tests in place,
you can run the tests.<topic_end>
<topic_start>
Run tests using IntelliJ or VSCode
The Flutter plugins for IntelliJ and VSCode support running tests.
This is often the best option while writing tests because it provides the
fastest feedback loop as well as the ability to set breakpoints.IntelliJVSCode<topic_end>
<topic_start>
Run tests in a terminal
To run the all tests from the terminal,
run the following command from the root of the project:To run all tests you put into one group,
run the following command from the root of the project:This example uses the group created in section 5.To learn more about unit tests, you can execute this command:
<topic_end>
<topic_start>Mock dependencies using Mockito
Sometimes, unit tests might depend on classes that fetch data from live
web services or databases. This is inconvenient for a few reasons:Therefore, rather than relying on a live web service or database,
you can “mock” these dependencies. Mocks allow emulating a live
web service or database and return specific results depending
on the situation.Generally speaking, you can mock dependencies by creating an alternative
implementation of a class. Write these alternative implementations by
hand or make use of the Mockito package as a shortcut.This recipe demonstrates the basics of mocking with the
Mockito package using the following steps:For more information, see the Mockito package documentation.<topic_end>
<topic_start>
1. Add the package dependencies
To use the mockito package, add it to the
pubspec.yaml file along with the flutter_test dependency in the