Update test_period_range.py
Attempting to implement test for resolved issue #21793

- [x] closes #21793
Hello @jnecus! 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 2020-05-15 09:07:12 UTC thanks @jnecus 