为什么我的模拟记录器显示为已调用但也没有？

Question

我第一次尝试在 WPF 应用程序中进行模拟。我正在测试的代码是 MVVM ViewModel 方法的一部分，如下所示：

try
{
    var airframesForRegistration = this.UnitOfWork.Airframes.GetAirframesForRegistration(this.SearchRegistration);
    this.currentAirframes = new ObservableCollection<Airframe>(airframesForRegistration);
}
catch (Exception ex)
{
    this.logger.Error($"Could not access the database", ex);
    throw;
}

我想测试一下

1. 错误被写入记录器服务和
2. 抛出异常。

为此，我使用 XUnit 和 Moq：

[Fact]
public void GetAirframesForSearchRegistration_DBAccessFail()
{
    using (var mock = AutoMock.GetLoose())
    {
        mock.Mock<IUnitOfWork>()
            .Setup(x => x.Airframes.GetAirframesForRegistration("AAAA"))
            .Throws(new DataException());

        string message = "Could not access the database";
        DataException exception = new DataException();

        mock.Mock<ILog>()
            .Setup(x => x.Error(message, exception));

        var afrvm = mock.Create<AirframesForRegistrationViewModel>();

        afrvm.SearchRegistration = "AAAA";

        Assert.Throws<DataException>(() => afrvm.GetAirframesForSearchRegistration());

        mock.Mock<ILog>()
            .Verify(x => x.Error(message, exception), Times.Exactly(1));

    }

因此测试失败：

Message: Moq.MockException : 
Expected invocation on the mock exactly 1 times, but was 0 times: x => x.Error("Could not access the database'", System.Data.DataException: Data Exception.)

Configured setups: 
ILog x => x.Error("Could not access the database", System.Data.DataException: Data Exception.)

Performed invocations: 
ILog.Warn("No Operators found in the database")
ILog.Warn("No airframe statuses found in the database")
ILog.Error("Could not access the database", System.Data.DataException: Data Exception.
   at Moq.MethodCall.Execute(Invocation invocation) in C:\projects\moq4\src\Moq\MethodCall.cs:line 120

（注意，额外的 ILog 警告出现在 ViewModel 的其他地方，我期待这些警告）。

问题

这意味着错误日志被调用了，但是测试失败了，因为它被调用了零次！如何设置 Moq 和 XUnit 以正确测试此场景？

Answer 1

记录器参数的设置是问题所在。

抛出的实例和预期的实例不同意味着它们在调用模拟时不会匹配。

模拟工作单元正在引发一个新异常。不是你所期待的。

[Fact]
public void GetAirframesForSearchRegistration_DBAccessFail() {
    using (var mock = AutoMock.GetLoose()) {
        //Arrange
        DataException exception = new DataException();

        mock.Mock<IUnitOfWork>()
            .Setup(x => x.Airframes.GetAirframesForRegistration("AAAA"))
            .Throws(exception);

        string message = "Could not access the database";

        mock.Mock<ILog>()
            .Setup(x => x.Error(message, exception));

        var afrvm = mock.Create<AirframesForRegistrationViewModel>();

        afrvm.SearchRegistration = "AAAA";

        //Act
        Action act = () => afrvm.GetAirframesForSearchRegistration();

        //Assert
        Assert.Throws<DataException>(act);

        mock.Mock<ILog>()
            .Verify(x => x.Error(message, exception), Times.Exactly(1));
    }
}

对于更宽松的期望，您可以使用 It.IsAny<> 参数匹配器

[Fact]
public void GetAirframesForSearchRegistration_DBAccessFail() {
    using (var mock = AutoMock.GetLoose()) {
        //Arrange
        mock.Mock<IUnitOfWork>()
            .Setup(x => x.Airframes.GetAirframesForRegistration("AAAA"))
            .Throws(new DataException());

        string message = "Could not access the database";

        mock.Mock<ILog>()
            .Setup(x => x.Error(message, It.IsAny<DataException>()));

        var afrvm = mock.Create<AirframesForRegistrationViewModel>();

        afrvm.SearchRegistration = "AAAA";

        //Act
        Action act = () => afrvm.GetAirframesForSearchRegistration();

        //Assert
        Assert.Throws<DataException>(act);

        mock.Mock<ILog>()
            .Verify(x => x.Error(message, It.IsAny<DataException>()), Times.Exactly(1));
    }
}