test for RecommenderXBlock

Please make the two parts of this function more explicit:
```python
url = reverse(
    'courseware_section',
    kwargs={
        'course_id': self.course.id.to_deprecated_string(),
        'chapter': 'Overview',
        'section': 'Welcome',
    }
)
check_for_get_code(self, code, reverse)
```
As an aside, I think the `check_for_get_code` function is needless indirection, and you'd be better off doing the assert here in this function. But if you really want to use it, I won't stop you.