Moq SetupSet on property - moq

Question

i am trying to learn to use Moq (4) to test the C# code below. I was hoping that by setting
mockTimer.SetupSet(m => m.Interval = It.IsInRange(
interval - shorter, interval + longer, Range.Inclusive));
before calling the method which assigns the interval property a value (ageService.AddParticipant method), the test would throw when an incorrect value was assigned. However, even when a value well outside the specified range is assigned to the Interval property within the AddParticipant method, the test passes. I also find timer.Interval has a value of 0 after executing the AddParticipant method, even though I can see this property being assigned a non-zero value when stepping through the AddParticipant method.
[TestMethod]
public void TestAgeUpdatingStartOnAdd()
{
var mockTimer = new Mock<IDispatcherTimer>();
mockTimer.SetupProperty(m => m.Interval);
mockTimer.Setup(m => m.Start());
mockTimer.Setup(m => m.Stop());
IDispatcherTimer timer = mockTimer.Object;
var ageService = new AgeUpdatingService(timer);
TimeSpan interval = TimeSpan.FromMinutes(10);
TimeSpan tolerance = TimeSpan.FromMilliseconds(100)
mockTimer.SetupSet(m => m.Interval = It.IsInRange(
interval - tolerance, interval + tolerance, Range.Inclusive));
ageService.AddParticipant(new Participant{ DOB = DateTime.Now + interval });
What am I doing wrong? Am I missing the point of the SetupSet method all together (and therefore should just stick to examining the properties on the timer object after executing the function, which seemed to work prior to placing the SetupSet method in the code)? If so, could you please explain what SetupSet exists for. Thank you.

Answer 1

Since you're creating your mock with new Mock<IDispatcherTimer>(), it defaults to Loose mock behavior. This means that the mock object will not complain when it is used in a way that was not specified via a Setup method. Using the constructor overload that accepts a MockBehavior enumeration and specifying Strict will make the code behave like you'd expect. It looks like that's how you're expecting to use it judging by the Setup calls; they would be unnecessary if you were using loose mocks.
Alternatively you can keep the loose mock and change the SetupSet for the Interval to be a VerifySet after you expect it to be set. I.e.:
var ageService = new AgeUpdatingService(timer);
TimeSpan interval = TimeSpan.FromMinutes(10);
TimeSpan tolerance = TimeSpan.FromMilliseconds(100)
ageService.AddParticipant(new Participant{ DOB = DateTime.Now + interval });
mockTimer.VerifySet(m => m.Interval = It.IsInRange(
interval - tolerance, interval + tolerance, Range.Inclusive));
This is like a test assertion, meaning if a set of the Interval property never happened when this is invoked, it would throw a MoqException and fail the test.

Answer 2

SetupSet can be used to setup a property setter - it is fairly unusual to need this, as arguments passed to Set typically don't need to be captured, as the calls to the Setter can be verified with a VerifySet after the "Act" step.
Here's a way to achieve what you want:
var mockTimer = new Mock<ITimer>();
// Simulate the actions of the Sut with the Mock
mockTimer.Object.Interval = 6;
mockTimer.Object.Interval = 7;
mockTimer.Object.Interval = 999;
// Ensure the mock was called in-band
mockTimer.VerifySet(m => m.Interval = It.IsInRange(5, 10, Range.Inclusive),
Times.Exactly(2));
// Ensure the mock was not called out of band
mockTimer.VerifySet(m => m.Interval = It.Is<int>(i => i < 5 || i > 10),
Times.Never);
Another, less elegant approach would be to use SetupSet to detect invalid invocations directly:
mockTimer.SetupSet(m => m.Interval = It.Is<int>(i => i < 5 || i > 10))
.Throws(new ArgumentOutOfRangeException());