Add a Python script that uses the PyTest API to run test discovery.

[ericsnowcurrently]

(for #4033)

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• [ ] Has sufficient logging.
• [ ] Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• [ ] Test plan is updated as appropriate
• [ ] package-lock.json has been regenerated by running npm install (if dependencies have changed)
• The wiki is updated with any design decisions/details.

[codecov]

Codecov Report

Merging #4605 into master will increase coverage by 20%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #4605     +/-   ##
========================================
+ Coverage      58%     77%    +20%     
========================================
  Files         369     445     +76     
  Lines       15946   21077   +5131     
  Branches     2507    3424    +917     
========================================
+ Hits         9134   16213   +7079     
+ Misses       6190    4858   -1332     
+ Partials      622       6    -616

Flag	Coverage Δ
#Linux	65% <ø> (?)
#Windows	66% <ø> (?)
#macOS	65% <ø> (?)