在 flutter/dart 中单元测试未来错误的正确方法是什么？

Question

我正在编写的单元测试应该因异常而失败，我想匹配使用匹配器抛出的错误，但我收到了一个错误。

我目前做错了什么，这里的错误是什么？如果我做错了，测试 returns 未来方法的错误场景的正确方法是什么？为什么会有异步间隙？

这是我要测试的方法：

Future<void> registerUser(String name, String email, String password) async {
auth.signUp(email, password, name).then((_) {
      auth.getCurrentUser().then((user) async {
        // Doing something
    }).catchError((onError) {
      throw onError;
    });

这是我写的测试：

test('should fail to register if fetching user fails', () async {
      MockAuth auth = MockAuth();
      RegisterRepository repo = RegisterRepository(auth);

      String password = 'password';
      String email = 'email';
      String name = 'name';

      when(auth.signUp(email, password, name))
          .thenAnswer((_) => Future.value());
      when(auth.getCurrentUser()).thenThrow((_) => throw Error());

      try {
        await repo.registerUser(name, email, password);
        fail('exception not thrown');
      } catch (e) {}

      verify(auth.signUp(email, password, name)).called(1);
      verify(auth.getCurrentUser()).called(1);
      verifyNoMoreInteractions(auth);
    });

我收到这个错误：

package:mockito/src/mock.dart 403:7               PostExpectation.thenThrow.<fn>
package:mockito/src/mock.dart 130:45              Mock.noSuchMethod
package:dive/repository/register_repo.dart 25:12  RegisterRepository.registerUser.<fn>
===== asynchronous gap ===========================
dart:async                                        Future.then
package:dive/repository/register_repo.dart 24:40  RegisterRepository.registerUser
test/repository/register_repo_test.dart 61:20     main.<fn>.<fn>

Closure: (dynamic) => Null

Answer 1

对于以后遇到此问题的任何其他人，

我把正在测试的方法中的async关键字去掉了，这里不需要async关键字。链接调用使其更具可读性：

Future<void> registerUser(String name, String email, String password) {
return auth
        .signUp(email, password, name)
        .then((_) => auth.getCurrentUser())
        .then((user) {
        // Doing something
    }).catchError((onError) {
      throw onError;
    });

要测试未来的错误，请执行以下操作：

test('should fail to register if fetching user fails', () async {
      MockAuth auth = MockAuth();
      RegisterRepository repo = RegisterRepository(auth);

      String password = 'password';
      String email = 'email';
      String name = 'name';

      when(auth.signUp(email, password, name))
          .thenAnswer((_) => Future.value());
      when(auth.getCurrentUser()).thenAnswer((_) => Future.error('error'));

      repo.registerUser(name, email, password).catchError((onError) {
        expect(onError.toString(), 'error');

        verify(auth.signUp(email, password, name)).called(1);
        verify(auth.getCurrentUser()).called(1);
        verifyNoMoreInteractions(auth);
      });
    });

测试现在通过了。

Answer 2

刚刚发现我们可以简单地做到这一点（查看 throwsA）：

test("getNews SHOULD throw an exception WHEN api fails", () {
  final ExceptionMock exception = ExceptionMock();
  when(() => newsApi.getNews()).thenAnswer((realInvocation) => Future<List<JsonNews>>.error(exception));

  expect(() => sut.getNews(), throwsA(exception));
});

请注意，我正在模拟异常。这样我就确信 api 确实被调用了。否则我不会捕获那个模拟的异常。使用具体对象时，无法确定是否返回值，因为依赖项实际上 returns 该对象或者它只是在 sun（被测系统）实现中硬编码。

在 flutter/dart 中单元测试未来错误的正确方法是什么？

What is the proper way to unittest future errors in flutter/dart?

asynchronous

dart

flutter

flutter-test