Using Verify to confirm expected parameter values in Moq mock class

If you upgrade to AutoFixture 2.9.1 (or newer) you can call the CreateProxy method on the Likeness instance which will emit a dynamic proxy for the destination type.

The generated dynamic proxy overrides Equals using Likeness which simplifies the syntax (quite a lot).

Here is the original test method, modified to use the Likeness proxy:

[Test]
public void TestSample()
{
    var foo = new Foo();
    var barMock = new Mock<IBar>();
    var expected = new A().AsSource().OfLikeness<A>().CreateProxy();
    expected.P1 = 1;

    foo.DoSomethingWith(barMock.Object);

    Assert.True(expected.Equals(foo.Data));     // passes
    barMock.Verify(m => m.Something(expected)); // passes
}

Note that it also makes the test assertion much more specific than accepting Any instance.

You can find more details on this new feature here.

In Verify Moq by default checks reference equality for arguments so it only passes when you provide the same instances (except if you've overriden Equals) in your tests and in your implementation.

In you case the expectedA.Value just returns the new A { P1 = 1 } created in the test which, of course, isn't the same instance created in DoSomethingWith.

You need to use Moq's It.Is construct to properly test this without overriding Equals (in fact for this you don't need Autofixture at all):

barMock.Verify(m => m.Something(It.Is<A>(arg => arg.P1 == a.P1)));

But if you have multiple properties like P1,P2,P3... AutoFixture can be useful:

barMock.Verify(m => m.Something(It.Is<A>(arg => expectedA.Equals(a))));

Because you don't need to write out the equality checks manually for all the properties.