Fixed issue with leftover test.json file

[jjames34]

• closes Doc build leaves behind a test.json file #19815
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[TomAugspurger]

Ideally, a user reading this doesn't have to care about any of the stuff with the IO buffer. They only care about writing and reading the dataframe.

I think it's best to leave the df.to_json and new_df = as it was previosly.

Then we can add a new ipython block afterwards to remove the file.

.. ipython:: python
   :suppress:

   import os
   os.remove('test.json')

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@c1237f2). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master   #19879   +/-   ##
=========================================
  Coverage          ?   91.65%           
=========================================
  Files             ?      150           
  Lines             ?    48915           
  Branches          ?        0           
=========================================
  Hits              ?    44835           
  Misses            ?     4080           
  Partials          ?        0

Flag	Coverage Δ
#multiple	90.03% <ø> (?)
#single	41.83% <ø> (?)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c1237f2...7927c6a. Read the comment docs.

[jreback]

pls change to using @TomAugspurger soln

[jreback]

thanks!