Moq: How to ensure Verify() reports on non-matching parameters - moq

Question

I have the following unit test verification using Moq:
var mock = new Mock<IDoSomethingUseful>();
var sut = new Thingy(mock.Object);
sut.CallDoSomethingUseful();
mock.Verify(
somethingUseful => somethingUseful.Move(
It.Is<MyVector>(
myVector => myVector.x == 123)), Times.Once, "This fail message needs to be hard-coded with myVector.x was not equal to 123");
How can I get Verify() to tell me that the predicate match failed? The test runner only reports that the call failed so I need to rely on the hard-coded message.

Answer 1

Using Callback the invocation arguments can be accessed. See section Callbacks here.
In your case you could add an expected value for x to the test and get the actual value in Callback. Finally use an Assert to verify if expected and actual values equal where the message can be formated using both values. HTH
int expected_x_value = 123;
int actual_x_value = 0;
var mock = new Mock<IDoSomethingUseful>();
mock.Setup(m => m.Move(It.IsAny<MyVector>()))
.Callback<MyVector>(
(v) =>
{
actual_x_value = v.x;
}
);
var sut = new Thingy(mock.Object);
sut.CallDoSomethingUseful();
Assert.AreEqual(expected_x_value, actual_x_value,
string.Format("myVector.x was expected to be called with x = '{0}' but was '{1}'",
expected_x_value, actual_x_value));