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 ?
All of these `# Test` comments seem needless if they are the first line of the test case function. It's only helpful if your test case function needs to do a bit of setup before doing the actual test -- but fortunately, you've organized your tests so that all of the setup happens in the `setUp()` function, which is great!