At work, we've been encouraged to find ways to open-source technologies that are useful but aren't core to our business.
While writing unit tests over the past several years, I developed some utilities that make it easier to perform some common test tasks, particularly when used with JMockit and EasyMock.
The utilities are now available as open source.
Update: The genius who develops JMockit has added so many features it's not necessary to use reflection to populate fields, so there's no need for TestUtils to be used with JMockit. TestUtils are still useful with other mocking tools, and when you just want to use reflection for something in a test where you aren't using mocking.