C# Unit Testing - Thread.Sleep(x) - How to Mock the System Clock

I have to test a method which does a certain amount of work after an interval.

while (running)
{
    ...
    // Work
    ...
    Thread.Sleep(Interval);
}

Interval is passed in as a parameter to the class so I can just pass in 0 or 1 but I was interested as to how to mock the system clock if this wasn't the case.

In my test I'd like to be able to simply set the time forward by TimeSpan Interval and have the thread wake up.

I've never written tests for code which acts upon the executing thread before and I'm sure there are some pitfalls to avoid - please feel free to elaborate on what approach you use.

Thanks!