How to TDD Asynchronous Events?
- by Padu Merloti
The fundamental question is how do I create a unit test that needs to call a method, wait for an event to happen on the tested class and then call another method (the one that we actually want to test)?
Here's the scenario if you have time to read further:
I'm developing an application that has to control a piece of hardware. In order to avoid dependency from hardware availability, when I create my object I specify that we are running in test mode. When that happens, the class that is being tested creates the appropriate driver hierarchy (in this case a thin mock layer of hardware drivers).
Imagine that the class in question is an Elevator and I want to test the method that gives me the floor number that the elevator is. Here is how my fictitious test looks like right now:
[TestMethod]
public void TestGetCurrentFloor()
{
var elevator = new Elevator(Elevator.Environment.Offline);
elevator.ElevatorArrivedOnFloor += TestElevatorArrived;
elevator.GoToFloor(5);
//Here's where I'm getting lost... I could block
//until TestElevatorArrived gives me a signal, but
//I'm not sure it's the best way
int floor = elevator.GetCurrentFloor();
Assert.AreEqual(floor, 5);
}
Edit:
Thanks for all the answers. This is how I ended up implementing it:
[TestMethod]
public void TestGetCurrentFloor()
{
var elevator = new Elevator(Elevator.Environment.Offline);
elevator.ElevatorArrivedOnFloor += (s, e) => { Monitor.Pulse(this); };
lock (this)
{
elevator.GoToFloor(5);
if (!Monitor.Wait(this, Timeout))
Assert.Fail("Elevator did not reach destination in time");
int floor = elevator.GetCurrentFloor();
Assert.AreEqual(floor, 5);
}
}
