I fixed the issue with stubbing mocks in the simplest way, that is by using Mockito.mock() instead of your custom solution that used ThreadLocalMockMethodInterceptor. I wrote test cases with mockito matchers for both spies and mocks. I'm used to writing test in bdd style so I hope you'd be fine with this, but I don't mind if you change them.
I also added test dependency to 'fest-assert'. If you're ok with it, it'd be nice to add it to parent-pom.
I wrote one addition test case for spies checking whether they are really injected in place of original objects because one of mine friends swore that he had problems with it. ;)