testcases for RecommenderXBlock

I messed things up in the previous PR, and thus I make a new one. I think I should also change cms/djangoapps/contentstore/views/component.py , but I forget how to do it. Do you know how to do that, and could you help me check is there any other thing wrong, @pmitros ?
This doesn't make sense here. The [`tearDown()`](https://docs.python.org/2.7/library/unittest.html#unittest.TestCase.tearDown) method is used to clean up after test cases, to keep every test independent from every other test. It is not used to add further assertions to test cases. (Since `tearDown()` is executed after every test, even if the test fails or raises an exception, this will often do the wrong thing in the case of failures.)

@jzoldak suggests (and I agree) that you copy this line into every test case where you want this check to happen. If that's every test case, then that's fine. Another alternative might be to try to write some kind of class decorator that automatically applies this line to the end of every test method, but that might be very tricky to write, debug, and understand after the fact, so copying the line into every test case is probably a better option.