How to test an NServiceBus handler that uses Schedule - nservicebus

Question

I'm playing with a simple handler that implements IWantToRunWhenBusStartsAndStops and in the start, it schedules a task like so:
public void Start()
{
_schedule.Every(TimeSpan.FromSeconds(5), Moo);
}
_schedule is injected via the constructor. The test I'm trying write is to make sure the task is scheduled when the handler starts. But I can't find a way to mock Schedule as it doesn't have a no-arg constructor and it doesn't implement an interface. I tried creating an actual instance of it with a mocked IBuilder but can't figure out what expectations to set on the IBuilder. Also, I looked at the source to see how they were testing Schedule but it looks like we're on an earlier version (v5.0.0 via nuget) because we don't have a DefaultScheduler which appears to be what they use in their current tests.

Answer 1

In fact NServiceBus team has already covered the scheduler with unit/acceptance test, i.e. there is no need to check whether the task was actually scheduled when your handler is executed. Instead you would probably want to unit test your handler itself, thus check if call to scheduler.Every() has been made. Here is simple example of how your unit test might look like:
[TestClass]
public class Tests
{
[TestMethod]
public void When_executing_handler_the_task_should_be_scheduled()
{
//arrange
var scheduler = new FakeSheduler();
//act
var handler = new TestHandler(scheduler);
handler.Start();
//assert
Assert.IsTrue(scheduler.WasCalled);
}
}
The handler itself:
class TestHandler: IWantToRunWhenBusStartsAndStops
{
readonly IMyScheduler _scheduler;
public TestHandler(IMyScheduler scheduler)
{
_scheduler = scheduler;
}
public void Start()
{
_scheduler.Every(TimeSpan.FromSeconds(5), () => { });
}
public void Stop() { }
}
Finally, you have to abstract from direct usage of NServiceBus scheduler in order to make it testable, here is the idea:
interface IMyScheduler
{
void Every(TimeSpan interval, Action action);
}
//your real implementation
class MySheduler: IMyScheduler
{
readonly Schedule _schedule;
public MySheduler(Schedule schedule)
{
_schedule = schedule;
}
public void Every(TimeSpan interval, Action action)
{
_schedule.Every(TimeSpan.FromSeconds(5), () => { });
}
}
//fake for the testing
class FakeSheduler: IMyScheduler
{
public bool WasCalled { get; set; }
public void Every(TimeSpan interval, Action action)
{
WasCalled = true;
}
}