TST: add arithmetic operators fixture
cc @jbrockmendel 

small work on this. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21033?src=pr&el=h1) Report
> Merging [#21033](https://codecov.io/gh/pandas-dev/pandas/pull/21033?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/36b8753e6ab94fb91c90901f0de631c51268dd65?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21033/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/21033?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21033      +/-   ##
==========================================
+ Coverage   91.82%   91.82%   +<.01%     
==========================================
  Files         153      153              
  Lines       49502    49502              
==========================================
+ Hits        45455    45457       +2     
+ Misses       4047     4045       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.22% <ø> (ø)` | :arrow_up: |
| #single | `41.88% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21033?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/21033/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.46% <0%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/21033/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.59% <0%> (+0.2%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21033?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/21033?src=pr&el=footer). Last update [36b8753...7588549](https://codecov.io/gh/pandas-dev/pandas/pull/21033?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
