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 would be nicer as a named tuple or similar
https://docs.python.org/2/library/collections.html#collections.namedtuple
STUDENT_INFO[0][0] is hard to interpret.