split Timestamp tests off of #19504
There is de-duplication/parametrization etc to be done, but that should wait until the tests are collected because we'll have to re-do it then anyway.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19511?src=pr&el=h1) Report
> Merging [#19511](https://codecov.io/gh/pandas-dev/pandas/pull/19511?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/69cd5fbfd8b57033b0eb280ebc6dd502652f269c?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/19511/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/19511?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19511      +/-   ##
==========================================
- Coverage   91.69%   91.67%   -0.03%     
==========================================
  Files         148      148              
  Lines       48561    48561              
==========================================
- Hits        44530    44518      -12     
- Misses       4031     4043      +12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.03% <ø> (-0.03%)` | :arrow_down: |
| #single | `41.72% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19511?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19511/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.22% <0%> (-1.74%)` | :arrow_down: |

------

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 this is fine, assuming you are going to completely destruct ``pandas/tests/tseries/test_timezones`` and put the tests in the appropriate places ? thanks! > this is fine, assuming you are going to completely destruct pandas/tests/tseries/test_timezones and put the tests in the appropriate places ?

Most of it will go into Timestamp/DatetimeIndex/...-specific modules.  There are some pieces that are more directly testing tslibs.timezones/tslibs.conversions, which can either stay in tests.tseries or go into a new tests.tslibs.