Unit testing with Moq method invoked inside of Task.Run

Question

I am trying to mock a service call inside of a method that I want to test.

The method body looks like this:

public string OnActionException(HttpActionContext httpRequest, Exception ex)
{
    var formattedActionException = ActionLevelExceptionManager.GetActionExceptionMessage(httpRequest);

    var mainErrorMessage = $"[{formattedActionException.ErrorId}]{formattedActionException.ErrorMessage}, {ex.Message}";

    this.LogError(mainErrorMessage, ex);

    if (this._configuration.MailSupportOnException)
        Task.Run(async () => await this._mailService.SendEmailForThrownException(this._configuration.SupportEmail, $"{mainErrorMessage} ---> Stack trace: {ex.StackTrace.ToString()}")); 

    return $"(ErrID:{formattedActionException.ErrorId}) {formattedActionException.ErrorMessage} {formattedActionException.KindMessage}";
}

What I am trying to mock inside my test is:

Task.Run(async () => await this._mailService.SendEmailForThrownException(this._configuration.SupportEmail, $"{mainErrorMessage} ---> Stack trace: {ex.StackTrace.ToString()}"));

The test method looks like this:

[TestMethod]
public void We_Send_System_Exception_On_Email_If_Configured_In_Settings()
{
    // arrange
    this._configurationWrapperMock.Setup(cwm => cwm.MailSupportOnException)
        .Returns(true);
    this._mailServiceMock.Setup(msm => msm.SendEmailForThrownException(It.IsAny<string>(), It.IsAny<string>()))
        .Returns(Task.FromResult(0));

    // act
    var logger = new ApiLogger(this._configurationWrapperMock.Object, this._mailServiceMock.Object);
    logger.OnActionException(
        new HttpActionContext(
            new HttpControllerContext()
            {
                Request = new HttpRequestMessage()
                {
                    Method = HttpMethod.Get,
                    RequestUri = new System.Uri("https://www.google.bg/")
                }
            }, 
            new ReflectedHttpActionDescriptor() { }
        ), 
        new System.Exception());

    // assert
    this._mailServiceMock.Verify(
        msm => msm.SendEmailForThrownException(It.IsAny<string>(), It.IsAny<string>()), 
        Times.Once);
}

The problem is that the method is never invoked, so my assert fails.

EDIT: I could change my question to: How do I need to re-write my method in order to make it testable?

Answer 1

I tried a simple, cut down version of your scenario above and the unit test consistently passes.

public interface IService
{
    Task<bool> Do();
}

public class AsyncService : IService
{
    public async Task<bool> Do()
    {
        return await Task.FromResult(true);
    }
}

public class MyClass
{
    private IService service;

    public MyClass(IService service)
    {
        this.service = service;
    }

    public async Task<bool> Run()
    {
        return await this.service.Do();
    }
}

[TestMethod]
public async Task TestAsyncMethod()
{
    Mock<IService> mockService = new Mock<IService>();
    mockService.Setup(m => m.Do()).Returns(Task.FromResult(false));

    MyClass myClass = new MyClass(mockService.Object);
    await myClass.Run();

    mockService.Verify(m => m.Do(), Times.Once);
}

It looks like you will need to make OnActionException return a Task<string> and then make the unit test asynchronous also. So rather than using Task.Run(), just return the await this._mailService.SendEmailForThrownException() in the OnActionException method.