Testing with Thread.sleep

What are the recommended approaches to using Thread.sleep() to speed up tests.

I am testing a network library with a retry functionality when connections are dropped or timeout errors occur, etc. The library however, uses a Thread.sleep() between the retries (so it won't connect thousands times while the server is restarting). The call is slowing the unit tests significantly, and I wonder what the options are to override it.

Note, I'm open to actually changing the code, or using a mocking framework to mock Thread.sleep(), but would like to hear your opinions/recommendation first.


  • It is usually a good idea to delegate time-related functionality to a separate component. That include getting the current time, as well as delays like Thread.sleep(). This way it is easy to substitute this component with mock during testing, as well as switch to a different implementation.