Unfortunately, dealing with legacy code means that the code is already written and the test-first approach won’t work. That’s ok, I have a little trick that I use. Just comment out the bodies of all the methods in the class you are about to test. Then write the tests that force you to uncomment the code. Just uncomment only enought to get the tests to pass, don’t uncomment anything you don’t have to. You have enough tests when all the code has been uncommented. The technique is almost as good as doing real test-first.

I have a dictionary.