Question

Can I test the assertion that an event was fired? Something like this:

[TestMethod]
public void EventFiresWhenChangingProperty()
{
    var sut = new SystemUnderTest();
    var eventRegister = new EventRegister(sut.PropertyChanged);
    sut.AnyProperty = "new value";
    Assert.EventWasFired(eventRegister);
}

Of course I could create an event handler, that puts some record into the test context or in an instance variable that is only read by this specific test but this seems a little bit too much plumbing. I am looking for something like the code above.

Answer 1

I usually hook up an anonymous method as an event listener, and set a testable value in it, like so:

var sut = new SystemUnderTest();
bool eventWasRaised = false;
sut.PropertyChanged += (s, e) => eventWasRaised = true;    
sut.AnyProperty = "new value";
Assert.IsTrue(eventWasRaised);

That gives a minimal amount of plumbing. If you want to add some cleaning up, you can create a variable holding the event handler:

var sut = new SystemUnderTest();
bool eventWasRaised = false;
EventHandler eh = (s, e) => eventWasRaised = true;
sut.PropertyChanged += eh;  // attach event handler
sut.AnyProperty = "new value";
Assert.IsTrue(eventWasRaised);
sut.PropertyChanged -= eh;  // detach event handler