CLN: Continued indexes/test_base.py cleanup
progress towards #20812
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20813?src=pr&el=h1) Report
> Merging [#20813](https://codecov.io/gh/pandas-dev/pandas/pull/20813?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8bee97a81764c5211d719d61a62424b1edfacd80?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/20813/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/20813?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #20813   +/-   ##
=======================================
  Coverage   91.77%   91.77%           
=======================================
  Files         153      153           
  Lines       49265    49265           
=======================================
  Hits        45215    45215           
  Misses       4050     4050
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.16% <ø> (ø)` | :arrow_up: |
| #single | `41.86% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20813?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/20813?src=pr&el=footer). Last update [8bee97a...1acfda1](https://codecov.io/gh/pandas-dev/pandas/pull/20813?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @WillAyd 