Why in the world is this Moq + NUnit test failing?

Question

I have this dataAccess mock object and I'm trying to verify that one of its methods is being invoked, and that the argument passed into this method fulfills certain constraints. As best I can tell, this method is indeed being invoked, and with the constraints fulfilled. This line of the test throws a MockException:

data.Verify(d => d.InsertInvoice(It.Is<Invoice>(i => i.TermPaymentAmount == 0m)), Times.Once());

However, removing the constraint and accepting any invoice passes the test:

data.Verify(d => d.InsertInvoice(It.IsAny<Invoice>()), Times.Once());

I've created a test windows form that instantiates this test class, runs its .Setup() method, and then calls the method which I am wishing to test. I insert a breakpoint on the line of code where the mock object is failing the test

data.InsertInvoice(invoice);

to actually hover over the invoice, and I can confirm that its .TermPaymentAmount decimal property is indeed zero at the time the method is invoked.

Out of desperation, I even added a call back to my dataAccess mock:

data.Setup(d => d.InsertInvoice(It.IsAny<Invoice>())).Callback((Invoice inv) => MessageBox.Show(inv.TermPaymentAmount.ToString("G17")));

And this gives me a message box showing 0. This is really baffling me, and no one else in my shop has been able to figure this out. Any help would be appreciated.

A barely related question, which I should probably ask independently, is whether it is preferable to use Mock.Verify() as I have here, or to use Mock.Expect(). Verifiable followed by Mock.VerifyAll() as I have seen other people doing? If the answer is situational, which situations would warrent the use of one over the other?

Answer 1

Just to rule this out (because I've got some strange behavior like you :
Try Times.Exactly(1) instead of Times.Once(). I've had some weird thing happening when using Times.Once() Though, I would have guessed that Once() is using Exactly(1) internally...

Answer 2

I am using version 3.1.0.0 of Moq and am not experiencing this issue with the following test case.

internal class Program
{
    private static void Main(string[] args)
    {
        var mock = new Mock<IData>();
        mock.Setup(d => d.InsertInvoice(It.IsAny<Invoice>()));

        var service = new MyService(mock.Object);
        service.DoSomething(new Invoice());

        mock.Verify(d => d.InsertInvoice(It.Is<Invoice>(i => i.TermPaymentAmount == 0m)), Times.Once());

        Console.ReadLine();
    }
}

internal class MyService
{
    private readonly IData _data;

    public MyService(IData data)
    {
        _data = data;
    }

    public void DoSomething(Invoice invoice)
    {
        _data.InsertInvoice(invoice);
    }
}

public class Invoice
{
    public decimal TermPaymentAmount { get; set; }
}

public interface IData
{
    void InsertInvoice(Invoice invoice);
}

Could you supply maybe a bit more information on how you are using the mock?

Answer 3

My guess is that it may have something to do with the problems inherent with equivalency checking of floating point values. Is your Invoice.TermPaymentAmount property value the result of a calculation, perhaps?

For an idea of what I'm talking about, see this possibly related question: http://stackoverflow.com/questions/485175/c-net-is-it-safe-to-check-floating-point-values-for-equality-to-0