TST: Use indices fixture in tests/indexes/test_base.py
part of #30914
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Something I've been trying to do that you might be interested in: these tests are a mix between using `indices` fixture and `self.create_index`.  If we take all of the create_index methods and put those indexes into the `indices` fixture, then we can switch over completely to using the fixture.
 Good idea @jbrockmendel, I can look into that. Is there a ticket for replacing `self.create_index`? +1 for renaming the fixture to `index` @simonjayhawkins 

I wonder about a good transition strategy though. I could create a fixture `index = indices` in `pandas/conftest.py` and then follow-up with a few PRs that replace `indices` by `index`. Wdyt? > +1 for renaming the fixture to `index` @simonjayhawkins
> 
> I wonder about a good transition strategy though. I could create a fixture `index = indices` in `pandas/conftest.py` and then follow-up with a few PRs that replace `indices` by `index`. Wdyt?

sounds good. that'll keep the diff here smaller here while allowing others to give their opinions on naming fixtures in general before making changes to other modules. A much more digestible diff now @simonjayhawkins :) I find `@pytest.mark.parametrize("index", ["string"], indirect=True)` much less clear than `index = tm.makeStringIndex(100)` @jbrockmendel I kinda agree. Instead of `tm.makeStringIndex(100)` we should use a `string_index` fixture though @jreback @jbrockmendel @simonjayhawkins 
As there seems to be no consent for `index` as an alternative name for `indices`, I refrained from introducing an alternative name in this PR altogether. This PR is exclusively using the `indices` fixture now. The renaming should come in follow-up PRs. @jreback CI is finally green sorry a small comment, also merge master and ping on green. @jreback Using indirect instead of a separate fixture now + CI is green thanks!

I think it’s worth mentioning in our contributing docs on how - when to use indirect fixtures  xref: #33128