Use pytest tmp file management fixtures instead of ensure_clean[_path|_dir]

[jgehrcke]

Opened as of discussion in #26818.

tests/io/test_pytables.py uses a context manager called ensure_clean_path. It might be worth using the pytest tmp_path fixture instead which I think provides everything we need with less code (also easier to understand for new contributors familiar with pytest). And it provides even a little more functionality, comparison:

• it guarantees file system isolation between tests (as does ensure_clean_path).
• it makes it obvious which file belongs to which test via expressive naming (as opposed to ensure_clean_path).
• it retains files for later inspection as opposed to ensure_clean_path. That can be useful for debugging after test failure.

Note: the pytest-managed temp files are removed in a rolling fashion across test runner invocations so that storage space requirement does not grow indefinitely with the number of invocations.

Cf. comment #26818 (comment)

[simonjayhawkins]

I think the issue should address pytest replacements for ensure_clean and ensure_clean_dir functions in pandas.util.testing and not just it's use in tests/io/test_pytables.py

+1 for using pytest fixtures thoughout.

[jreback]

@jgehrcke I am pretty ok with doing this change, does it require a specific version min for pytest?; we should update the docs in contributing.rst (not sure if we have any text about this though)

[simonjayhawkins]

I am pretty ok with doing this change

probably not all at once? used in many places.

does it require a specific version min for pytest?

we'll probably want to use the newer tmp_path which returns a pathlib.Path (in python < 3.6 this is a pathlib2.Path) instead of the older tmpdir which returns a py.path.local path object.

tmp_path (and tmp_path_factory) were added in pytest 3.9.0

[jreback]

we should do this post dropping 3.5 (I don't know if we have an issue for that yet).

[simonjayhawkins]

fair enough. dropping py3.5 probably not far away, but probably OK to use when adding new tests/fixtures?

did use tmp_path in filepath_or_buffer fixture in tests\io\formats\test_format.py #27598