Moq Lambda表达式表现异常

Question

I have a unit test using MOQ that's behaving unexpectedly. I'm expecting the IsAuthorizedAsync method to always return true, but it's returning false. Here's a simplified version of the code that's adding the IsAuthorizedAsync method to my Mock Object.

    public static IAuthenticationInterface GetAuthentication()
    {
       var mock = new Mock<IAuthenticationInterface>();
       mock.Setup(e => e.IsAuthorizedAsync(It.IsIn<string>(), It.IsAny<MyEvent>())).Returns(System.Threading.Tasks.Task.FromResult(true)).Verifiable();

       // return the mock object
       return mock.Object;
   }

Here's code similar to the code that's using it:

bool isAuthorized = this.mockObject != null && await this.mockObject.IsAuthorizedAsync("abc123", myEvent).ConfigureAwait(false);

Like I said, it's returning false when it looks to me like it should always return true. Is there any way for me to step into the lambda expression code? Alternatively, is there any way for me to view what the actual lambda expression that's being used when I call this.mockObject.IsAuthorizedAsync? I suspect it's not what I think it is.

-Eric

Answer 1

As per @tzachs' comment, note that the It.IsIn matcher takes a list of matching values (strings in your instance). It.IsIn() with an empty params or IEnumerable will never match anything, as it is implemented with .Contains :

public static TValue IsIn<TValue>(IEnumerable<TValue> items)
{
   return Match.Create<TValue>((Predicate<TValue>) 
     (value => Enumerable.Contains<TValue>(items, value)), 
     (Expression<Func<TValue>>) (() => It.IsIn<TValue>(items)));
}

hence the failure to return the desired result. You'll want to either change this eg

It.IsAny<string>() // ... Any string at all
It.Is<string>(s => s == "Foo") // ... Match via a Predicate
It.IsIn<string>("Foo", "Bar", "Baz") // ... Match via a List

Also, note that when working with Async methods, that Moq (and Test Frameworks like NUnit and XUnit) have support for Async semantics. So instead of 'hacking' a Task.FromResult , what you can do instead is:

[Test]
public async void MyTest()  // ... The UT can be made async
{
    var mock = new Mock<IAuthenticationInterface>();
    mock.Setup(e => e.IsAuthorizedAsync(It.IsIn<string>("Foo"), It.IsAny<MyEvent>()))
            .ReturnsAsync(true)  // ... Async
            .Verifiable();

    // async calls can be awaited
    Assert.True(await mock.Object.IsAuthorizedAsync("Foo", null));
}

(and yes, I know I'm just testing the Mock here :)