Most common (anti-)pattern

I guess that by now everyone knows that Singleton is considered mostly harmful and definitely overused. Many people have said that it hinders testing but there is nothing more convincing that unit test that completes fine on its own but mysteriously fails when whole suite is launched. It looks strange when even after doing reset() and adding new when() rules the mock created by Mockito behaves in wrong way. It is a lot less mysterious when you find a singleton that was injected with mock object on class load and ignores the fact that whole Spring context was created and destroyed multiple times ever since.