Mocking Extension Methods with Moq

Question

I have a preexisting Interface...

public interface ISomeInterface {     void SomeMethod(); } 

and I've extended this intreface using a mixin...

public static class SomeInterfaceExtensions {     public static void AnotherMethod(this ISomeInterface someInterface)     {         // Implementation here     } } 

I have a class thats calling this which I want to test...

public class Caller {     private readonly ISomeInterface someInterface;      public Caller(ISomeInterface someInterface)     {         this.someInterface = someInterface;     }      public void Main()     {         someInterface.AnotherMethod();     } } 

and a test where I'd like to mock the interface and verify the call to the extension method...

    [Test]     public void Main_BasicCall_CallsAnotherMethod()     {         // Arrange         var someInterfaceMock = new Mock<ISomeInterface>();         someInterfaceMock.Setup(x => x.AnotherMethod()).Verifiable();          var caller = new Caller(someInterfaceMock.Object);          // Act         caller.Main();          // Assert         someInterfaceMock.Verify();     } 

Running this test however generates an exception...

System.ArgumentException: Invalid setup on a non-member method: x => x.AnotherMethod() 

My question is, is there a nice way to mock out the mixin call?

Answer 1

I have used a Wrapper to get around this problem. Create a wrapper object and pass your mocked method.

See Mocking Static Methods for Unit Testing by Paul Irwin, it has nice examples.