How do you unit test Rx operators that use timers?

Question

There are a number of operators that are timer based, and I although I don't have a concrete example, would think it common to create new operators that utilise timers. So how would you go about writing a test that runs synchronously for these operators?

As an example, how could I go about unit testing an operator such as BufferWithTime?

Answer 1

The most accessible way to do the test would be to use TestScheduler:

var source = new Subject<int>();
var scheduler = new TestScheduler();

var outputValues = new List<IList<int>>();

source
    .BufferWithTime(TimeSpan.FromTicks(500), scheduler)
    .Subscribe(x => outputValues.Add(x));

scheduler.RunTo(1);
source.OnNext(1);

scheduler.RunTo(100);
source.OnNext(2);

scheduler.RunTo(200);
source.OnNext(3);

scheduler.RunTo(501);
source.OnNext(4);

scheduler.RunTo(1001);

Assert.AreEqual(2, outputValues.Count);
Assert.AreEqual(3, outputValues[0].Count);
Assert.AreEqual(1, outputValues[1].Count);

In addition you can also use a bunch of types from System.Reactive.Testing.dll, which makes things even easier but takes a dependency on Microsoft.VisualStudio.QualityTools.UnitTestFramework.dll which in turn has a dependency on System.Web.dll (not available in the client profile).

// using System.Reactive.Testing;
// using System.Reactive.Testing.Mocks;

var scheduler = new TestScheduler();

var source = scheduler.CreateColdObservable(
    new Recorded<Notification<int>>(0, new Notification<int>.OnNext(1)),
    new Recorded<Notification<int>>(100, new Notification<int>.OnNext(2)),
    new Recorded<Notification<int>>(400, new Notification<int>.OnNext(3)),
    new Recorded<Notification<int>>(500, new Notification<int>.OnNext(4))
    )
    .BufferWithTime(TimeSpan.FromTicks(500), scheduler);

var observer = new MockObserver<IList<int>>(scheduler);

source.Subscribe(observer);

scheduler.RunTo(1001);

Assert.AreEqual(2, observer.Count);
Assert.AreEqual(3, observer[0].Value.Value.Count);
Assert.AreEqual(1, observer[1].Value.Value.Count);