CLN: tests/window/*
* Renamed `test_window.py` to `test_win_type.py`
* Added `'count'` to `arithmetic_win_operators`
* Reused fixtures
* Used more pytest idioms in `test_moments_consistency_expanding.py`

Hello @mroeschke! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:











There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-11-18 17:41:06 UTC thanks @mroeschke 