TST: Test aggregation over arrays (#3788)

[mroeschke]

• closes Aggregating over arrays #3788
• tests added / passed
• passes git diff upstream/master | flake8 --diff

[jreback]

you are picking up the commit for the pivot table PR. this should be separate

[TomAugspurger]

@mroeschke specifically, the workflow should be

• sync your master with upstream git fetch upstream; git rebase upstream/master from your master branch
• checkout a new branch for each change git co -b array-agg

You should just be able to git rebase -i upstream/master and delete the commit with the pivot table changes and force push.

[mroeschke]

Ah didn't notice this picked up the commit from my other PR. Thanks for the guidance! I'll decouple it later tonight.

[codecov-io]

Current coverage is 85.21% (diff: 100%)

Merging #14675 into master will increase coverage by <.01%

@@             master     #14675   diff @@
==========================================
  Files           143        143          
  Lines         50787      50787          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43273      43276     +3   
+ Misses         7514       7511     -3   
  Partials          0          0          

Powered by Codecov. Last update f26b049...01dce9d

[mroeschke]

I checked out the travis-ci build logs and it doesn't look like my change directly caused the build to fail (to my knowledge). Is there anything I need to address on my end?

EDIT: Reran the tests, and they are now passing

[jreback]

thanks!