Run Isort on tests/indexes P4/Final
- [x] partial #23334
- [x] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
Run `isort -rc pandas/tests/indexes/`

PR is capped at 20 files. So this is not all the files modified from `pandas/tests/indexes/`. So this is Part Four  ( last pr) of this directory `pandas/tests/indexes/`. 
Hello @thoo! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_arithmetic.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_arithmetic.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_asfreq.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_asfreq.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_astype.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_astype.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_construction.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_construction.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_formats.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_formats.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_indexing.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_indexing.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_ops.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_ops.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_partial_slicing.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_partial_slicing.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_period.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_period.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_period_range.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_period_range.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_scalar_compat.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_scalar_compat.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_setops.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_setops.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_tools.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/period/test_tools.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/test_base.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/test_base.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/test_category.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/test_category.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/test_frozen.py`](https://github.com/thoo/pandas/blob/f982261bca22e997b15e7c880ccebcd725c505ab/pandas/tests/indexes/test_frozen.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23343?src=pr&el=h1) Report
> Merging [#23343](https://codecov.io/gh/pandas-dev/pandas/pull/23343?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/caea25a8b91d62b30eef99aa0c523448e19cd6db?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23343/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23343?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23343   +/-   ##
=======================================
  Coverage   92.22%   92.22%           
=======================================
  Files         169      169           
  Lines       51261    51261           
=======================================
  Hits        47277    47277           
  Misses       3984     3984
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.66% <ø> (ø)` | :arrow_up: |
| #single | `42.23% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23343?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23343?src=pr&el=footer). Last update [caea25a...a929602](https://codecov.io/gh/pandas-dev/pandas/pull/23343?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 needs a rebase thanks @thoo 