TST: clean up some tests issues & style
closes #18037 
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@b36dab5`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `70%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18232/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #18232   +/-   ##
=========================================
  Coverage          ?   91.41%           
=========================================
  Files             ?      163           
  Lines             ?    50091           
  Branches          ?        0           
=========================================
  Hits              ?    45791           
  Misses            ?     4300           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.22% <70%> (?)` | |
| #single | `40.36% <20%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `91.17% <100%> (ø)` | |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `88.17% <64.7%> (ø)` | |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `95% <66.66%> (ø)` | |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.48% <75%> (ø)` | |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.42% <80%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18232?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/18232?src=pr&el=footer). Last update [b36dab5...c20332c](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@b36dab5`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `70%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18232/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #18232   +/-   ##
=========================================
  Coverage          ?   91.41%           
=========================================
  Files             ?      163           
  Lines             ?    50091           
  Branches          ?        0           
=========================================
  Hits              ?    45791           
  Misses            ?     4300           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.22% <70%> (?)` | |
| #single | `40.36% <20%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `91.17% <100%> (ø)` | |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `88.17% <64.7%> (ø)` | |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `95% <66.66%> (ø)` | |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.48% <75%> (ø)` | |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.42% <80%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18232?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/18232?src=pr&el=footer). Last update [b36dab5...c20332c](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=h1) Report
> Merging [#18232](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b36dab50a5dc7ca2d8de2b62a81014e095117771?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `70%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18232/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18232      +/-   ##
==========================================
+ Coverage    91.4%   91.41%   +<.01%     
==========================================
  Files         163      163              
  Lines       50091    50091              
==========================================
+ Hits        45788    45791       +3     
+ Misses       4303     4300       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.22% <70%> (+0.02%)` | :arrow_up: |
| #single | `40.36% <20%> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `91.17% <100%> (ø)` | :arrow_up: |
| [pandas/core/dtypes/cast.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2Nhc3QucHk=) | `88.17% <64.7%> (ø)` | :arrow_up: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `95% <66.66%> (ø)` | :arrow_up: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.48% <75%> (ø)` | :arrow_up: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.42% <80%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/18232/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.2% <0%> (+1.81%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18232?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/18232?src=pr&el=footer). Last update [b36dab5...c20332c](https://codecov.io/gh/pandas-dev/pandas/pull/18232?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
