REF/TST: Collect Straggler Arithmetic Tests
After this AFAICT there are only 5 files left with possibly-misplaced arithmetic tests.  Leaving those for another pass since some of them are testing type-specific behavior so will need a careful look.

Moved tests are unchanged except for contextifying pytest.raises where appropriate.

There's a hackathon in Feb I'm vaguely planning to use as a time to try to de-duplicate/parametrize the tests that have been moved to tests.arithmetic with TODO notes.
Hello @jbrockmendel! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/test_datetime64.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/arithmetic/test_datetime64.py) !

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/test_numeric.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/arithmetic/test_numeric.py) !

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/test_period.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/arithmetic/test_period.py) !

 - There are no PEP8 issues in the file [`pandas/tests/arithmetic/test_timedelta64.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/arithmetic/test_timedelta64.py) !

 - There are no PEP8 issues in the file [`pandas/tests/frame/test_arithmetic.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/frame/test_arithmetic.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/period/test_ops.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/indexes/period/test_ops.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/test_base.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/indexes/test_base.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/test_range.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/indexes/test_range.py) !

 - There are no PEP8 issues in the file [`pandas/tests/indexes/timedeltas/test_arithmetic.py`](https://github.com/jbrockmendel/pandas/blob/3024963d84ff4681c2188a35757bdbf080b9995f/pandas/tests/indexes/timedeltas/test_arithmetic.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24376?src=pr&el=h1) Report
> Merging [#24376](https://codecov.io/gh/pandas-dev/pandas/pull/24376?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5d134ec1a9ab118abbd16157bd161783547117e6?src=pr&el=desc) will **decrease** coverage by `49.31%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24376/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24376?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #24376       +/-   ##
===========================================
- Coverage   92.29%   42.98%   -49.32%     
===========================================
  Files         162      162               
  Lines       51841    51841               
===========================================
- Hits        47847    22282    -25565     
- Misses       3994    29559    +25565
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `42.98% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24376?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY2F0ZWdvcmljYWwucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvY29udmVydGVyLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `0% <0%> (-98.65%)` | :arrow_down: |
| [pandas/core/groupby/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9jYXRlZ29yaWNhbC5weQ==) | `0% <0%> (-95.46%)` | :arrow_down: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `0% <0%> (-91.17%)` | :arrow_down: |
| [pandas/io/sas/sas\_xport.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfeHBvcnQucHk=) | `0% <0%> (-90.15%)` | :arrow_down: |
| [pandas/core/tools/numeric.py](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvdG9vbHMvbnVtZXJpYy5weQ==) | `10.44% <0%> (-89.56%)` | :arrow_down: |
| ... and [120 more](https://codecov.io/gh/pandas-dev/pandas/pull/24376/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24376?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/24376?src=pr&el=footer). Last update [5d134ec...f19026c](https://codecov.io/gh/pandas-dev/pandas/pull/24376?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/24376?src=pr&el=h1) Report
> Merging [#24376](https://codecov.io/gh/pandas-dev/pandas/pull/24376?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5d134ec1a9ab118abbd16157bd161783547117e6?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24376/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24376?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24376   +/-   ##
=======================================
  Coverage   92.29%   92.29%           
=======================================
  Files         162      162           
  Lines       51841    51841           
=======================================
  Hits        47847    47847           
  Misses       3994     3994
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.7% <ø> (ø)` | :arrow_up: |
| #single | `42.98% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24376?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/24376?src=pr&el=footer). Last update [5d134ec...38e7f1f](https://codecov.io/gh/pandas-dev/pandas/pull/24376?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!