TST: adding join_types fixture
follow up for PR #20059

Extracting join types to a fixture

- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Hello @almaleksia! Thanks for updating the PR.

































Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on March 12, 2018 at 23:23 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20287?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@31afaf8`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20287/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/20287?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #20287   +/-   ##
=========================================
  Coverage          ?   91.73%           
=========================================
  Files             ?      150           
  Lines             ?    49168           
  Branches          ?        0           
=========================================
  Hits              ?    45102           
  Misses            ?     4066           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.11% <ø> (?)` | |
| #single | `41.86% <ø> (?)` | |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20287?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/20287?src=pr&el=footer). Last update [31afaf8...9dabfc1](https://codecov.io/gh/pandas-dev/pandas/pull/20287?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @almaleksia keep em coming!

if you are looking for things........want to make tz a top-level fixture (prob need to name it something different though as the name tz is pretty common), e.g.

https://github.com/pandas-dev/pandas/blob/master/pandas/tests/indexes/datetimes/test_timezones.py#L244 (and many other very similar lines of code).
 @jreback sure, thank you for the feedback. I'll make PR. I also wanted to take splitting pandas/tests/frame/test_indexing.py  :D 