[CLN] parametrize and cleanup a bunch of tests
Hello @jbrockmendel! Thanks for updating the PR.





























Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on July 28, 2018 at 16:31 Hours UTC comments and pls rebase # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22093?src=pr&el=h1) Report
> Merging [#22093](https://codecov.io/gh/pandas-dev/pandas/pull/22093?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/0b7a08b70444056f964bb636a74ac41ca0058d37?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22093/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22093?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22093      +/-   ##
==========================================
- Coverage   92.06%   92.05%   -0.01%     
==========================================
  Files         170      170              
  Lines       50705    50705              
==========================================
- Hits        46680    46678       -2     
- Misses       4025     4027       +2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.46% <ø> (-0.01%)` | :arrow_down: |
| #single | `42.3% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22093?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/22093/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `85.47% <0%> (-0.21%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22093?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/22093?src=pr&el=footer). Last update [0b7a08b...d7d2e26](https://codecov.io/gh/pandas-dev/pandas/pull/22093?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks