Adds more test cases

[burkestar]

RATIONALE

While using the tool, I noticed there was a long list of false positives and was curious why. I added some simple test cases for situations that weren't covered yet with the goal of better understanding what this plugin does and does not support.

TESTING

Tested with:

tox -e py38

with result:

============================================================================================================================= test session starts ==============================================================================================================================
platform darwin -- Python 3.8.5, pytest-6.1.0, py-1.9.0, pluggy-0.13.1
cachedir: .tox/py38/.pytest_cache
rootdir: /Users/dustin/Developer/open_source/pytest-deadfixtures
plugins: deadfixtures-2.2.1
collected 22 items

tests/test_deadfixtures.py .....................x                                                                                                                                                                                                                        [100%]

======================================================================================================================== 21 passed, 1 xfailed in 1.34s =========================================================================================================================```

[jllorencetti]

Hi @burkestar thank you for taking some time to help me improve the project, I appreciate! :)
One small suggestion, what do you think about instead of asserting for a wrongful condition, mark the test with xfail and linking the reason to the issue link?

[burkestar]

Thanks for the suggestion @jllorencetti! Let me know if there's anything else you'd like to see here. Thanks for this nice package to help us identify unused fixtures.