TST: partial indexing with __getitem__ and integer labels
 - [x] closes #12416
 - [x] tests added / passed
 - [x] passes ``git diff master --name-only -- '*.py' | flake8 --diff``
 - [ ] whatsnew entry

Just a test for the bug, which was fixed at some time in the past.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16029?src=pr&el=h1) Report
> Merging [#16029](https://codecov.io/gh/pandas-dev/pandas/pull/16029?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/90dd3f94cf120f628c086fdd965fc82878951bd9?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/16029/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/16029?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #16029   +/-   ##
=======================================
  Coverage   90.99%   90.99%           
=======================================
  Files         153      153           
  Lines       50469    50469           
=======================================
  Hits        45924    45924           
  Misses       4545     4545
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.76% <ø> (ø)` | :arrow_up: |
| #single | `40.43% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16029?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/16029?src=pr&el=footer). Last update [90dd3f9...dcc5acd](https://codecov.io/gh/pandas-dev/pandas/pull/16029?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 still reviewing. @toobaz Can you add the `df[[1]]` raising a KeyError case as well? (that also was incorrect at the time you opened the issue) > @toobaz Can you add the df[[1]] raising a KeyError case as well? (that also was incorrect at the time you opened the issue)

yep, done @toobaz Thanks!