MAINT: Remove pytest.warns in tests

[gfyoung]

Per discussion in #18258, we are prohibiting its use in tests, at least for the time being.

[gfyoung]

I added the linting but will push fix in second commit once I confirm linting works.

[jreback]

@gfyoung this needs to fix the test, no? ) (or maybe you are just testing if this will fail)

(pandas) bash-3.2$ grep -r -E --include '*.py' 'pytest\.warns' pandas/tests/
pandas/tests//series/test_timeseries.py:        with pytest.warns(FutureWarning):

[gfyoung]

(or maybe you are just testing if this will fail)

@jreback : Yes, that's the plan 😉 You can see that it worked.

https://travis-ci.org/pandas-dev/pandas/jobs/331740919#L3018

[codecov]

Codecov Report

Merging #19341 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #19341      +/-   ##
==========================================
- Coverage   91.57%   91.54%   -0.03%     
==========================================
  Files         150      150              
  Lines       48702    48702              
==========================================
- Hits        44597    44585      -12     
- Misses       4105     4117      +12

Flag	Coverage Δ
#multiple	89.91% <ø> (-0.03%)	⬇️
#single	41.71% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
pandas/plotting/_converter.py	65.22% <0%> (-1.74%)	⬇️

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[gfyoung]

@jreback : Lint error has been patched as planned. PTAL.

[jreback]

thanks @gfyoung

I would not necessarily be averse to changing to use pytest.warns generally. I don't know if it has any diffs with what we have now.

[jorisvandenbossche]

I would not necessarily be averse to changing to use pytest.warns generally. I don't know if it has any diffs with what we have now.

The main difference (I think) is that ours has check_stacklevel for deprecation/future warnings