TST: Cleanup tests/indexes/test_base.py

[WillAyd]

This module could use some major refactoring. Approach outlined with checkboxes below - will add or modify as we go through:

• Parametrize the existing module where appropriate
  • Pass 1: TST: Parametrized index tests #20624
  • Pass 2: CLN: Continued indexes/test_base.py cleanup #20813
  • Pass 3: Base Index Tests Cleanup Part 3 #20931
  • Pass 4: Parametrization of indexes/test_base #4 #20979
• Replace any class methods / attributes with fixtures where appropriate
• Move tests into new modules / sub-modules (ex: TST: Parametrized index tests #20624 (comment), TST: Parametrized index tests #20624 (comment), Base Index Tests Cleanup Part 3 #20931 (comment))
• Add fixture for fill arguments (see Base Index Tests Cleanup Part 3 #20931 (comment))

[jbrockmendel]

All the PRs linked in the OP are merged, and I've done several passes on this file since then too. Closing.