Add testing support for postgres

[dwhswenson]

This works locally, although it may take some work to get it running in the CI workflow.

• Opted for direct install of postgres, since that seemed easier than Docker.
• Switch which backend you're using by setting the env var EXORCIST_TEST_DB; sqlite (default) or postgres
  • All tests will run; only the ones that build off the fresh_db (which is most of them) will switch database backend. Obviously, tests of from_filename are still using SQLite even if you request postgres.
• multiple devtools scripts created, partly for future flexibility, mainly for convenience when testing locally
  • separate install and create stages because create is more likely to be reused again locally than install (e.g., delete the directory that contains the DB)
  • extra postgres 1-liners for restart and stop mainly so I don't have to look up the pg_ctl documentation (since I probably won't even remember that the command is called pg_ctl).

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.20% 🎉

Comparison is base (c0722a5) 91.44% compared to head (2efdc46) 91.65%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #31      +/-   ##
==========================================
+ Coverage   91.44%   91.65%   +0.20%     
==========================================
  Files           7        7              
  Lines         526      539      +13     
==========================================
+ Hits          481      494      +13     
  Misses         45       45              

Files Changed	Coverage Δ
exorcist/tests/test_taskstatusdb.py	99.34% <100.00%> (+0.02%)	⬆️

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[richardjgowers]

@mikemhenry is probably going to be the CI wizard here getting postgres hooked up

@dwhswenson rather than toggling between sqlite/other backends, could instead the fixture just look for a $POSTGRES_BACKEND env variable and skip testing postgres if not found? This will be frustrating to test multiple backends at once otherwise

[mikemhenry]

If this is working then I am not sure if you need me to do anything, but this is how I did this in the past:

https://github.com/samplchallenges/SAMPL-league/blob/main/.github/workflows/CI.yml#L23-L38

Then just used the standard stuff with pytest/django testing but I think what David has setup makes it easier to run tests locally if you don't want to use your system's postgress or run a container locally