PEP8: test/indexes/base
- [x] passes `git diff upstream/master | flake8 --diff`

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13771?src=pr) is 84.57% (diff: 100%)

> No coverage report found for **master** at b60e42b.
> 
> Powered by [Codecov](https://codecov.io?src=pr). Last update [b60e42b...05b2691](https://codecov.io/gh/pydata/pandas/compare/b60e42b02040624f319cadd60a99fe50eb62d62e...05b26914b8dc6066614b00a0be9fd78c4070d832?src=pr)
 thanks @sinhrks 
