TST: Remove groupby/test_function.py

[rhshadrach]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

This finishes up the removal of test_function.py from the groupby tests. With the exception of test_groupby_non_arithmetic_agg_int_like_precision (which is moved to other files here), the tests that remained fall into two (and partially overlapping) camps:

• Tests for numeric_only
• Tests that use the fixture groupby_func, which goes over every groupby operation

For the first, the options I considered were creating test_numeric_only.py or split it up into various other files such as test_reductions.py, test_cumlative.py, and some others. Similarly, for tests that use groupby_func that don't fit in other files, I considered creating test_all_methods.py (which can be renamed to something better) or split up the tests into several different files.

I'm completely on the fence here. Breaking up a parameterized test and duplicating code across multiple files seems pretty bad. While I don't love having test_all_methods (it's sort of a catch-all), at first it seemed to me that it is less bad than breaking up the parameterized tests. But then grepping around, it appears that there are only three tests across all of groupby that would go in test_all_methods. Perhaps this is something we can expand on later - but maybe since there are so few tests it's okay to break these up?

Any ideas here are very much welcome.

cc @jbrockmendel @mroeschke

[rhshadrach]

This tests has been cleaned up and not just moved.

[rhshadrach]

This tests has been cleaned up and not just moved.

[WillAyd]

looks reasonable to me. nice work

[mroeschke]

Breaking up a parameterized test and duplicating code across multiple files seems pretty bad. While I don't love having test_all_methods (it's sort of a catch-all), at first it seemed to me that it is less bad than breaking up the parameterized tests.

IMO I think in the future this could be rolled into a potential refactor of test_groupby.py as a file testing "groupby scenarios that should work with all methods"

[mroeschke]

Thanks @rhshadrach

[rhshadrach]

Breaking up a parameterized test and duplicating code across multiple files seems pretty bad. While I don't love having test_all_methods (it's sort of a catch-all), at first it seemed to me that it is less bad than breaking up the parameterized tests.

IMO I think in the future this could be rolled into a potential refactor of test_groupby.py as a file testing "groupby scenarios that should work with all methods"

Sounds good - test_groupby is my next target; I've always been under the impression that tests here should be for something like "All groupby attributes that aren't ops and don't have a more specific location". E.g. len(df.groupby(...)) or df.groupby(...).groups. I think it makes sense to roll test_all_methods into here.