Fix slow tests to not actually sleep

These two tests were causing the unit tests to take 2min40secs to run.  The
fix is to patch time.sleep because we don't actually actually need to sleep
during the tests.

I also updated the tests to be more idiomatic including:

* Don't need to define setUp() if you're just calling super()
* Prefer assertRaises(), this gives better failure messages
 and is easier to read.

cc @danielgtaylor