Hey,

the tests are still wrong, sorry. Here you're testing nothing useful. You don't even take the result of findByUnknown!!!

I already told you what you should do here, and I will repeat once again:
* add numbers using addUnknown
* find them using substrings and full strings, check that you get them
* call clearUnknown
* check that you don't find anything

Please do proper unit tests by _thinking_ about what you want to test.

If you still can't do proper unit tests while I'm in holiday next week, I'll do them myself because I really want to see this committed.