TST: test for categorical index monotonicity
- xref occasional failures here: https://travis-ci.org/MacPython/pandas-wheels/jobs/259998677
- incorrect version detection in #17142 of bottleneck
> just to check, is this changing behaviour? or just additional tests / faster implementation? (as I don't fully understand the link with the failing tests)

nothing changed. I *thought* it was doing something incorrectly, but appears to be ok. in py2.7-32 something is going wrong occasionally, not sure what exactly. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=h1) Report
> Merging [#17152](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f4330611ff5ac1cbb4a89c4a7dab3d0900f9e64a?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17152/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17152      +/-   ##
==========================================
- Coverage   91.01%      91%   -0.02%     
==========================================
  Files         162      162              
  Lines       49497    49503       +6     
==========================================
- Hits        45051    45050       -1     
- Misses       4446     4453       +7
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.78% <100%> (ø)` | :arrow_up: |
| #single | `40.26% <57.14%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/category.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9jYXRlZ29yeS5weQ==) | `98.53% <100%> (+0.02%)` | :arrow_up: |
| [pandas/core/nanops.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbmFub3BzLnB5) | `98.03% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.66% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/config\_init.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29uZmlnX2luaXQucHk=) | `96.06% <0%> (+1.57%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17152?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/17152?src=pr&el=footer). Last update [f433061...30c6281](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=h1) Report
> Merging [#17152](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/f4330611ff5ac1cbb4a89c4a7dab3d0900f9e64a?src=pr&el=desc) will **decrease** coverage by `0.03%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17152/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17152      +/-   ##
==========================================
- Coverage   91.01%   90.97%   -0.04%     
==========================================
  Files         162      162              
  Lines       49497    49501       +4     
==========================================
- Hits        45051    45036      -15     
- Misses       4446     4465      +19
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.75% <100%> (-0.02%)` | :arrow_down: |
| #single | `40.26% <66.66%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `95.93% <100%> (ø)` | :arrow_up: |
| [pandas/core/indexes/category.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9jYXRlZ29yeS5weQ==) | `98.52% <100%> (+0.01%)` | :arrow_up: |
| [pandas/core/nanops.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbmFub3BzLnB5) | `98.03% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.23% <0%> (-1.82%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.66% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/config\_init.py](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvY29uZmlnX2luaXQucHk=) | `96.06% <0%> (+1.57%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17152?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/17152?src=pr&el=footer). Last update [f433061...30c6281](https://codecov.io/gh/pandas-dev/pandas/pull/17152?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
