Split test fixtures in test_filter_metadata.py

[ilumsden]

Minor issue that cropped up in the review of #164.

In test_filter_metadata.py, there are the following 3 functions:

• filter_one_column
• filter_multiple_and
• filter_multiple_or

These functions are essentially test fixtures, but, instead of being treated as fixtures, they are just functions that are combined into one fixture called test_filter_metadata. As a result of having this "super-fixture", we can't easily detect which of the 3 functions above actually failed.

This "super-fixture" should be split into 3 different fixtures to test these functions independently and simplify failure tracking.

Additionally, per the discussion in #164, these functions are (for some reason) also used in:

• thicket/tests/test_concat_thickets.py
• thicket/tests/test_groupby.py

As a result, these functions should be moved into some "testing utils" module. Then, test_filter_metadata.py should import the functions and use them in the 3 new fixtures, and the other two modules (listed above) should import the functions and use them as they currently are.