~Finish collecting m8[ns] tests, start collecting division by zero tests
The division by zero tests aren't yet parametrized, are mostly just moved as-is.  Both these and the newly moved m8[ns] tests will need a bunch of de-duplication in the next pass.

Tons of DataFrame tests failing.  #22074 is the PR we need, though maybe not the one we deserve.

Started in on fixtures.
k, rebase on top as merged #22074 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22153?src=pr&el=h1) Report
> Merging [#22153](https://codecov.io/gh/pandas-dev/pandas/pull/22153?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/def50e26f78c507a743fa11fee98230412ae50a8?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/22153/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/22153?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22153      +/-   ##
==========================================
+ Coverage   92.06%   92.06%   +<.01%     
==========================================
  Files         169      169              
  Lines       50694    50694              
==========================================
+ Hits        46671    46672       +1     
+ Misses       4023     4022       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.47% <ø> (ø)` | :arrow_up: |
| #single | `42.32% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22153?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/22153/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `96.43% <0%> (+0.05%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22153?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/22153?src=pr&el=footer). Last update [def50e2...29c9738](https://codecov.io/gh/pandas-dev/pandas/pull/22153?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 One build is failing because it says there is no "box" fixture, but there is.  Seen this before?
<b>update</b> never mind, dumb mistake on my part. @jreback this should go before others for easiest rebasing ok lgtm. can you rebase and merge on green (just to make sure). can you make the next followup to split this to a sub-dir (i know its all td atm but just to make it clear / easier)