TST: test_nanops some parametrize & catch warnings (RuntimeWarning: All-Nan slice in tests)
closes #20011 
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20484?src=pr&el=h1) Report
> Merging [#20484](https://codecov.io/gh/pandas-dev/pandas/pull/20484?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/add37ac877ac1632080347f7521c7f164d3e3647?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20484/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/20484?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #20484      +/-   ##
==========================================
- Coverage   91.85%   91.82%   -0.03%     
==========================================
  Files         152      152              
  Lines       49232    49231       -1     
==========================================
- Hits        45221    45206      -15     
- Misses       4011     4025      +14
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.21% <ø> (-0.03%)` | :arrow_down: |
| #single | `41.83% <ø> (-0.05%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20484?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/20484/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.07% <0%> (-1.74%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/20484/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.52% <0%> (-0.21%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/20484/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.18% <0%> (-0.01%)` | :arrow_down: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
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