Functionalize tests for test_plots.py (#285)
Functionalize tests for test_plots.py (#285)

* Change tests to function pattern

* Fix linting errors

* Further split apart fixtures

* Rename fixture to be more direct

* Rename parameter to be more direct

arviz-devs/arviz,arviz-devs/arviz,arviz-devs/arviz,arviz-devs/arviz