TST (string dtype): update all tests in tests/frame/indexing

[jorisvandenbossche]

This removes most xfails in pandas/tests/frame/indexing. The remaining xfails are actually bugs that need to be fixed (i.e. can't be fixed by just a test update)

The main case that I encountered here is when starting from an empty DataFrame, and then adding columns:

df = pd.DataFrame()
df["a"] = values

will result in an object-dtype columns Index object (because we start with object dtype for the empty frame, and then preserve that dtype when inserting labels).

And when constructing the expected result through a default pd.DataFrane(.., columns=["a"]), you get the future string dtype for the columns Index.

xref #54792

[mroeschke]

Thanks @jorisvandenbossche

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 2.3.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 bec2dbca274a4f983790d069279a4b3aec184f49

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #60193: TST (string dtype): update all tests in tests/frame/indexing'

4. Push to a named branch:

git push YOURFORK 2.3.x:auto-backport-of-pr-60193-on-2.3.x

5. Create a PR against branch 2.3.x, I would have named this PR:

"Backport PR #60193 on branch 2.3.x (TST (string dtype): update all tests in tests/frame/indexing)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

[jorisvandenbossche]

Manual backport -> #60212