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dev_dependencies section.This example also uses the http package,
so define that dependency in the dependencies section.mockito: 5.0.0 supports Dart’s null safety thanks to code generation.
To run the required code generation, add the build_runner dependency
in the dev_dependencies section.To add the dependencies, run flutter pub add:<topic_end>
<topic_start>
2. Create a function to test
In this example, unit test the fetchAlbum function from the
Fetch data from the internet recipe.
To test this function, make two changes:The function should now look like this:
<code_start>Future<Album> fetchAlbum(http.Client client) async {
final response = await client
.get(Uri.parse('https://jsonplaceholder.typicode.com/albums/1'));
if (response.statusCode == 200) {
// If the server did return a 200 OK response,
// then parse the JSON.
return Album.fromJson(jsonDecode(response.body) as Map<String, dynamic>);
} else {
// If the server did not return a 200 OK response,
// then throw an exception.
throw Exception('Failed to load album');
}
}<code_end>
In your app code, you can provide an http.Client to the fetchAlbum method
directly with fetchAlbum(http.Client()). http.Client() creates a default
http.Client.<topic_end>
<topic_start>
3. Create a test file with a mock http.Client
Next, create a test file.Following the advice in the Introduction to unit testing recipe,
create a file called fetch_album_test.dart in the root test folder.Add the annotation @GenerateMocks([http.Client]) to the main
function to generate a MockClient class with mockito.The generated MockClient class implements the http.Client class.
This allows you to pass the MockClient to the fetchAlbum function,
and return different http responses in each test.The generated mocks will be located in fetch_album_test.mocks.dart.
Import this file to use them.
<code_start>import 'package:http/http.dart' as http;
import 'package:mocking/main.dart';
import 'package:mockito/annotations.dart';
// Generate a MockClient using the Mockito package.
// Create new instances of this class in each test.
@GenerateMocks([http.Client])
void main() {
}<code_end>
Next, generate the mocks running the following command:<topic_end>
<topic_start>
4. Write a test for each condition
The fetchAlbum() function does one of two things:Therefore, you want to test these two conditions.
Use the MockClient class to return an “Ok” response
for the success test, and an error response for the unsuccessful test.
Test these conditions using the when() function provided by
Mockito:
<code_start>import 'package:flutter_test/flutter_test.dart';
import 'package:http/http.dart' as http;
import 'package:mocking/main.dart';
import 'package:mockito/annotations.dart';
import 'package:mockito/mockito.dart';
import 'fetch_album_test.mocks.dart';
// Generate a MockClient using the Mockito package.
// Create new instances of this class in each test.
@GenerateMocks([http.Client])
void main() {
group('fetchAlbum', () {
test('returns an Album if the http call completes successfully', () async {
final client = MockClient();
// Use Mockito to return a successful response when it calls the
// provided http.Client.
when(client
.get(Uri.parse('https://jsonplaceholder.typicode.com/albums/1')))
.thenAnswer((_) async =>
http.Response('{"userId": 1, "id": 2, "title": "mock"}', 200));
expect(await fetchAlbum(client), isA<Album>());
});
test('throws an exception if the http call completes with an error', () {
final client = MockClient();
// Use Mockito to return an unsuccessful response when it calls the
// provided http.Client.
when(client
.get(Uri.parse('https://jsonplaceholder.typicode.com/albums/1')))
.thenAnswer((_) async => http.Response('Not Found', 404));
expect(fetchAlbum(client), throwsException);
});
});
}<code_end>
<topic_end>
<topic_start>
5. Run the tests
Now that you have a fetchAlbum() function with tests in place,
run the tests.You can also run tests inside your favorite editor by following the
instructions in the Introduction to unit testing recipe.<topic_end>
<topic_start>
Complete example
<topic_end>
<topic_start>lib/main.dart
<code_start>import 'dart:async';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
Future<Album> fetchAlbum(http.Client client) async {
final response = await client
.get(Uri.parse('https://jsonplaceholder.typicode.com/albums/1'));
if (response.statusCode == 200) {
// If the server did return a 200 OK response,