TST: confirming tests for some fixed issues
closes #7710, closes #8617, closes #13119

Closes a few issues still tagged with 0.19.0 that only need a confirming test

## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/14117?src=pr) is 85.27% (diff: 100%)

> Merging [#14117](https://codecov.io/gh/pydata/pandas/pull/14117?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will increase coverage by **<.01%**

``` diff
@@             master     #14117   diff @@
==========================================
  Files           139        139          
  Lines         50543      50543          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43101      43102     +1   
+ Misses         7442       7441     -1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [8fdfa51...252facb](https://codecov.io/gh/pydata/pandas/compare/8fdfa518105cde9ae16449578b3d75c13c8c19a5...252facb89ba974203661705429db145017e37851?src=pr)
 @jorisvandenbossche #6817 is not the right issue. can you update. (at the top of the PR)
 @jreback whoops, updated (the commit message contained the correct number)
