Unit test type_polarities

[EmileTrotignon]

The file type_polarities is a critical part of sherlodoc, but it is not tested.

Such tests would be primarily useful as documentation that is guaranteed to stay up to date.

To understand how to do such unit tests, you can look the query/test directory. Most of the tests in that dir are generated randomly, which is not necessary here (and would also be hard to do).