How should I write unit tests for a method uses timer?

Question

I've written a method that waits for 5 seconds, how should I write unit tests for it to ensure that it has waited for 5 seconds?

public IObservable<Unit> Wait(CancellationToken token)
        {
            var unit = Observable.Return(Unit.Default);

            lock (Locker)
            {
                if (Waited)
                    return unit;

                Waited= true; 

                unit = Observable.Timer(TimeSpan.FromSeconds(5))
                    .Select(_ => Unit.Default)
                    .RunAsync(token);
            }

            return unit;
        }

Answer 1

You can use the StopWatch class to measure time or just take current time before and after the method is called and assert that 5 seconds or more passed.

For example:

using Shouldly;

var watch = StopWatch.StartNew();
Wait() // call your function
watch.stop();
watch.Elapsed.Seconds.ShouldBeGreaterThanOrEqualTo(5);

or

Assert.IsTrue(watch.Elapsed.Seconds> 5, "The time was not greater than five");