# 使用 Mockito 模拟依赖关系 > 使用 Mockito package 在测试中模拟服务端行为。 Sometimes, unit tests might depend on classes that fetch data from live web services or databases. This is inconvenient for a few reasons: 某些情况下，单元测试可能会依赖需要从线上 Web 服务或数据库中获取数据的类。 这样会带来一些不便，原因如下： * Calling live services or databases slows down test execution. 访问线上服务或数据库会拖慢测试执行效率。 * A passing test might start failing if a web service or database returns unexpected results. This is known as a "flaky test." 原本可以通过的测试可能会失败， 因为 Web 服务或数据库可能会返回不符合预期的结果。 这种情况被称作“flaky test”。 * It is difficult to test all possible success and failure scenarios by using a live web service or database. 使用线上 web 服务或数据库来测试很难覆盖全所有可能成功或失败的场景。 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. 因此，最好不要依赖线上 web 服务或数据库，我们可以把这些依赖“模拟（mock）”出来 。 模拟（Mocks）允许我们仿造一个线上服务或数据库，并且可以根据条件返回特定结果。 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. 通常来说，可以通过创建类的另一种实现来模拟（mock）这种依赖。 类的另一种实现可以手写，也可以借助 [Mockito package](https://pub-web.flutter-io.cn/packages/mockito)， 后者简单一些。 This recipe demonstrates the basics of mocking with the Mockito package using the following steps: 本篇教程介绍了 Mockito package 的基本用法，可以参考以下步骤： ## Directions ## 使用步骤 1. Add the package dependencies. 添加 `mockito` 和 `test` 依赖 2. Create a function to test. 创建一个要测试的函数 3. Create a test file with a mock `http.Client`. 创建一个模拟了 `http.Client` 的测试文件 4. Write a test for each condition. 给每一个条件写一个测试 5. Run the tests. 执行这些测试 For more information, see the [Mockito package][] documentation. 更多信息可以查阅 [Mockito][Mockito package] package 的官方文档。 ## 1. Add the package dependencies ## 1. 添加 package 依赖 To use the `mockito` package, add it to the `pubspec.yaml` file along with the `flutter_test` dependency in the `dev_dependencies` section. 为了使用 mockito package，首先将其和 `flutter_test` 的依赖一起添加到 `pubspec.yaml` 文件的 `dev_dependencies` 部分： This example also uses the `http` package, so define that dependency in the `dependencies` section. 本例中还使用了 `http` package，需要添加到 `dependencies` 部分： `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. 感谢代码生成，`mockito: 5.0.0` 已经支持了 Dart 的空安全。 要运行所需的代码生成工具，请将 `build_runner` 依赖添加到 `dev_dependencies` 项目下。 To add the dependencies, run `flutter pub add`: 运行 `flutter pub add` 添加依赖： ```console $ flutter pub add http dev:mockito dev:build_runner ``` ## 2. Create a function to test ## 2. 创建一个要测试的函数 In this example, unit test the `fetchAlbum` function from the [Fetch data from the internet][] recipe. To test this function, make two changes: 本例中，我们要对 [获取网络数据][Fetch data from the internet] 章节的 `fetchAlbum` 函数进行单元测试。 为了便于测试，我们需要做两个改动： 1. Provide an `http.Client` to the function. This allows providing the correct `http.Client` depending on the situation. For Flutter and server-side projects, provide an `http.IOClient`. For Browser apps, provide an `http.BrowserClient`. For tests, provide a mock `http.Client`. 给函数提供一个 `http.Client`。这样的话我们可以在不同情形下提供相应的 `http.Client` 实例。如果是 Flutter 以及服务端项目， 可以提供 `http.IOClient `。如果是浏览器应用， 可以提供 `http.BrowserClient`。为了测试， 我们要提供一个模拟的 `http.Client`。 2. Use the provided `client` to fetch data from the internet, rather than the static `http.get()` method, which is difficult to mock. 使用上面提供的 `client` 来请求网络数据， 不要用 `http.get()` 这个静态方法，因为它比较难以模拟。 The function should now look like this: 函数经过改动之后： ```dart Future 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); } else { // If the server did not return a 200 OK response, // then throw an exception. throw Exception('Failed to load album'); } } ``` 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`. ## 3. Create a test file with a mock `http.Client` ## 3. 创建一个模拟了 http.Client 的测试文件 Next, create a test file. 接下来，创建一个测试文件。 Following the advice in the [Introduction to unit testing][] recipe, create a file called `fetch_album_test.dart` in the root `test` folder. 遵循 [单元测试介绍][Introduction to unit testing] 章节的建议， 我们在根目录下的 `test` 文件夹中创建一个名字为 `fetch_post_test.dart` 的文件。 Add the annotation `@GenerateMocks([], customMocks: [MockSpec(as: #MockHttpClient)])` to the main function to generate a `MockHttpClient` class with `mockito`. 在 main 函数上添加一个 `@GenerateMocks([], customMocks: [MockSpec(as: #MockHttpClient)])` 注解以生成含有 `mockito` 的 `MockHttpClient` 类。 The generated `MockHttpClient` class implements the `http.Client` class. This allows you to pass the `MockHttpClient` to the `fetchAlbum` function, and return different http responses in each test. `MockHttpClient` 类实现了 `http.Client` 类。 如此一来，我们就可以把 `MockHttpClient` 传给 `fetchAlbum` 函数， 还可以在每个测试中返回不同的 http 请求结果。 The generated mocks will be located in `fetch_album_test.mocks.dart`. Import this file to use them. 生成的 mock 文件将会放在 `fetch_album_test.mocks.dart`，请导入以使用它。 ```dart 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. // Note: Naming the generated mock `MockHttpClient` to avoid confusion with // `MockClient` from `package:http/testing.dart`. @GenerateMocks([], customMocks: [MockSpec(as: #MockHttpClient)]) void main() { } ``` Next, generate the mocks running the following command: ```console $ dart run build_runner build ``` ## 4. Write a test for each condition ## 4. 给每一个条件写一个测试 The `fetchAlbum()` function does one of two things: 回过头来看，`fetchPost()` 函数会完成下面两件事中的一件： 1. Returns an `Album` if the http call succeeds 如果 http 请求成功，返回 `Post` 2. Throws an `Exception` if the http call fails 如果 http 请求失败，抛出 `Exception` Therefore, you want to test these two conditions. Use the `MockHttpClient` class to return an "Ok" response for the success test, and an error response for the unsuccessful test. 因此，我们要测试这两种条件。可以使用 `MockHttpClient` 类为成功的测试返回一个 "OK" 的请求结果， 为不成功的测试返回一个错误的请求结果。 Test these conditions using the `when()` function provided by Mockito: 我们使用 Mockito 的 `when()` 函数来达到以上目的： ```dart 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. // Note: Naming the generated mock `MockHttpClient` to avoid confusion with // `MockClient` from `package:http/testing.dart`. @GenerateMocks([], customMocks: [MockSpec(as: #MockHttpClient)]) void main() { group('fetchAlbum', () { test('returns an Album if the http call completes successfully', () async { final client = MockHttpClient(); // 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()); }); test('throws an exception if the http call completes with an error', () { final client = MockHttpClient(); // 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); }); }); } ``` ## 5. Run the tests ## 5. 执行测试 Now that you have a `fetchAlbum()` function with tests in place, run the tests. 现在我们有了一个带测试的 `fetchAlbum()` 函数，开始执行测试！ ```console $ flutter test test/fetch_album_test.dart ``` You can also run tests inside your favorite editor by following the instructions in the [Introduction to unit testing][] recipe. 你也可以参考 [单元测试介绍][Introduction to unit testing] 章节用自己喜欢的编辑器来执行测试。 ## Complete example ## 完整的样例 ##### lib/main.dart ```dart import 'dart:async'; import 'dart:convert'; import 'package:flutter/material.dart'; import 'package:http/http.dart' as http; Future 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); } else { // If the server did not return a 200 OK response, // then throw an exception. throw Exception('Failed to load album'); } } class Album { final int userId; final int id; final String title; const Album({required this.userId, required this.id, required this.title}); factory Album.fromJson(Map json) { return Album( userId: json['userId'] as int, id: json['id'] as int, title: json['title'] as String, ); } } void main() => runApp(const MyApp()); class MyApp extends StatefulWidget { const MyApp({super.key}); @override State createState() => _MyAppState(); } class _MyAppState extends State { late final Future futureAlbum; @override void initState() { super.initState(); futureAlbum = fetchAlbum(http.Client()); } @override Widget build(BuildContext context) { return MaterialApp( title: 'Fetch Data Example', theme: ThemeData( colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple), ), home: Scaffold( appBar: AppBar(title: const Text('Fetch Data Example')), body: Center( child: FutureBuilder( future: futureAlbum, builder: (context, snapshot) { if (snapshot.hasData) { return Text(snapshot.data!.title); } else if (snapshot.hasError) { return Text('${snapshot.error}'); } // By default, show a loading spinner. return const CircularProgressIndicator(); }, ), ), ), ); } } ``` ##### test/fetch_album_test.dart ```dart 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. // Note: Naming the generated mock `MockHttpClient` to avoid confusion with // `MockClient` from `package:http/testing.dart`. @GenerateMocks([], customMocks: [MockSpec(as: #MockHttpClient)]) void main() { group('fetchAlbum', () { test('returns an Album if the http call completes successfully', () async { final client = MockHttpClient(); // 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()); }); test('throws an exception if the http call completes with an error', () { final client = MockHttpClient(); // 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); }); }); } ``` ## Summary ## 总结 In this example, you've learned how to use Mockito to test functions or classes that depend on web services or databases. This is only a short introduction to the Mockito library and the concept of mocking. For more information, see the documentation provided by the [Mockito package][]. 通过本例，我们已经学会了如何用 Mockito 来测试对 web 服务或数据库有依赖的函数或类。 这里只是简短地介绍了 Mockito 库以及模拟（mocking）的概念。 更多内容请移步至 [Mockito package][]。 [Fetch data from the internet]: /cookbook/networking/fetch-data [Introduction to unit testing]: /cookbook/testing/unit/introduction [Mockito package]: https://pub-web.flutter-io.cn/packages/mockito