如何断言某个方法仅被调用一次？

Question

[Subject(typeof(OnceADayProcessor))]
public class When_processing_process_twice
{
    private static ICanBeProcessedOnceADay ProcessedOnceADay;

    private Establish context = () => { OnceADayProcessor.Now = () => new DateTime(2011, 1, 1, 0, 0, 0, 0); };

    private Because of = () =>
                             {
                                 ProcessedOnceADay = MockRepository.GenerateMock<ICanBeProcessedOnceADay>();
                                 ProcessedOnceADay.Process();
                                 ProcessedOnceADay.Process();
                             };

    private It should_execute = () => ProcessedOnceADay.AssertWasCalled(x => x.Expect(p => p.Process()));
    private It should_execute_only_once = () => ProcessedOnceADay.AssertWasNotCalled(x => x.Expect(p => p.Process()));
}

编辑后的解决方案：

[Subject(typeof(OnceADayProcessor))]
public class When_processing_a_process_twice_at_the_same_day
{
    static ICanBeProcessedOnceADay canBeProcessedOnceADay;

    Establish context = () =>
    {
        canBeProcessedOnceADay = A.Fake<ICanBeProcessedOnceADay>();
    };

    Because of = () =>
    {
        OnceADayProcessor.Process(canBeProcessedOnceADay);
        OnceADayProcessor.Process(canBeProcessedOnceADay);
    };

    It should_execute_only_once = () => 
        A.CallTo(() => canBeProcessedOnceADay.Process()).MustHaveHappened(Repeated.Exactly.Once);
}

Answer 1

var mock = MockRepository.GenerateMock<ICanBeProcessedOnceADay>();
mock.Expect(a => a.Process()).Repeat.Times(1);
...
mock.VerifyAllExpectations();

Answer 2

我将对 stub.Expect() 和 stub.VerifyAllExpectations() 的调用替换为 stub.AssertWasCalled(x => x.Process(), o =>It 中的 o.Repeat.Once())。如果您对存根有多个期望，则可以将每个断言放入一个 It 中，并让它们彼此独立地失败（或成功）。

存根的创建将进入Establish（本质上，任何依赖项和被测系统的创建是单元测试中“安排”阶段的一部分）。

另请考虑不要使用 GenerateMock 而是使用 GenerateStub，因为当您调用 Expect 指定的方法以外的其他方法时，模拟可能会导致脆弱的测试。像 FakeItEasy 这样的库通常提供更好、更容易发现的 API，更容易学习，并且会让你掉进“成功的坑”。

Answer 3

如果你想确保一个方法仅被调用一次，你需要一个严格的模拟：

var mock = MockRepository.GenerateStrictMock<IShouldOnlyBeCalledOnce>();
mock.Expect(a => a.Process()).Repeat.Once();

sut.Process(mock)

mock.VerifyAllExpectations();

如果你只使用GenerateMock，它会执行一个“至少”检查。这也适用于 Repeats.Times(x) 。