Reference parameter in virtual method doesn't update correctly when class is mocked

[iitaiy]

I have test that check ref parameter value from event that raised after the change. The test work fine when I create real class but when I try mocked class its fail. Simple code example:

[TestClass]
public class Fixture
{
    [TestMethod]
    public void CheckRealClass()
    {
        // this test passed
        var classToTest = new NumberChangerClass();
        CheckClass(classToTest);
    }

    [TestMethod]
    public void CheckMockedClass()
    {
        // this test failed
        var classToTest = new Mock<NumberChangerClass>() { CallBase = true };
        CheckClass(classToTest.Object);
    }

    private void CheckClass(NumberChangerClass numberChangerClass)
    {
        // Arrange
        var number = 1;
        numberChangerClass.StorageChanged += (sender, args) =>
        {
            Assert.AreEqual(2, number);
        };


        // Act
        numberChangerClass.SetValue(ref number, 2);
    }
}

public class NumberChangerClass
{
    public event EventHandler StorageChanged;

    public virtual void SetValue(ref int storage, int newValue)
    {
        storage = newValue;
        StorageChanged?.Invoke(this, null);
    }
}

In CheckMockedClass the number is actually changed but only after the the code exits from SetValue method.

Thank you for the help.

[stakx]

Near-duplicate of #466.

@iitaiy, the behaviour you are observing is a direct consequence of how DynamicProxy (which Moq depends on) handles by-reference parameters during method call interception (which is documented at https://github.com/castleproject/Core/blob/master/docs/dynamicproxy-by-ref-parameters.md): Arguments are buffered in a separate location during call interception and only written back at the end of interception, that's why refparameters are updated in a delayed / deferred manner. There is unfortunately nothing that can be done about it.

Thank you for taking the time to report this, though!