Add downstream tests and guard against leakages across tests

[MatthewFlamm]

closes #43 and closes #50

[codecov-commenter]

Codecov Report

Merging #49 (5132b9d) into main (ca5b4dd) will decrease coverage by 0.73%. The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main      #49      +/-   ##
==========================================
- Coverage   92.85%   92.13%   -0.73%     
==========================================
  Files           2        2              
  Lines          84       89       +5     
==========================================
+ Hits           78       82       +4     
- Misses          6        7       +1     

Impacted Files	Coverage Δ
pytest_pyvista/pytest_pyvista.py	91.95% <80.00%> (-0.73%)	:arrow_down:

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[MatthewFlamm]

Two image regression failures, which need to be investigated.

One failure related to different verify_image_cache objects being passed. This one could be more serious.

[MatthewFlamm]

tests/plotting/test_plotting.py::test_closing_and_mem_cleanup - RuntimeError: tests/plotting/image_cache/plot_1.png does not exist in image cache

This is the error in the test where the verify_image_cache object doesn't match in the traceback. It is referring to an image for a different test. Wondering if this could be related to fix in https://github.com/pyvista/pyvista/pull/4102.

[akaszynski]

@MatthewFlamm, we ready for another patch release?

[MatthewFlamm]

See #53