Separate tick tests, use pytest parametrize
The test output for offsets would be more useful of the tests were parametrized.  So this PR implements that for about a third of the tests.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=h1) Report
> Merging [#18233](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/40fd6b4045b7241d5aedc20e2427c68bd4797312?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18233/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18233      +/-   ##
==========================================
- Coverage   91.43%   91.41%   -0.02%     
==========================================
  Files         164      163       -1     
  Lines       50091    50091              
==========================================
- Hits        45800    45791       -9     
- Misses       4291     4300       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.22% <ø> (ø)` | :arrow_up: |
| #single | `40.39% <ø> (-0.04%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/reshape/reshape.py](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9yZXNoYXBlLnB5) | `99.27% <0%> (-0.73%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/api.py](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXBpLnB5) | `100% <0%> (ø)` | :arrow_up: |
| [pandas/tseries/offsets.py](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvb2Zmc2V0cy5weQ==) | `97.11% <0%> (ø)` | :arrow_up: |
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `96.39% <0%> (ø)` | :arrow_up: |
| [pandas/core/reshape/melt.py](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZWx0LnB5) | | |
| [pandas/core/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY2F0ZWdvcmljYWwucHk=) | `95.79% <0%> (+0.04%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18233?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/18233?src=pr&el=footer). Last update [40fd6b4...bc4147d](https://codecov.io/gh/pandas-dev/pandas/pull/18233?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Implemented most of the requests.  Left some of the parametrization and fixturization for later.

In working with the offsets module I'm finding more bugs (e.g #18235).  I'd like to wrap this up for now, fix+test some of those, then circle back to this. pls do this: https://github.com/pandas-dev/pandas/pull/18233#discussion_r150418107 you need to add the new dir in setup.py (test section) need to move the ``pandas/tests/tseries/data`` dir to ``offsets``. you can test locally on these to find these issue before pushing FYI. Ha that’s a polite way of pointing out a screwup.  My bad, will rectify. so you also need to modify ``setup.py`` to reflect the moved ``data`` dir; the build test checks this. ping on green. thanks!