Test snapshots

[VisruthSK]

Swap some tests to use snapshots. Should be discussed.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.25%. Comparing base (c0e7c35) to head (53afd19).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1170      +/-   ##
==========================================
+ Coverage   91.14%   91.25%   +0.10%     
==========================================
  Files          15       15              
  Lines        6065     6070       +5     
==========================================
+ Hits         5528     5539      +11     
+ Misses        537      531       -6     

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[jgabry]

Thank you! At first glance this looks good. I'll take another look soon to take a closer look at exactly which tests we're converting to snapshots.

For now a question: if we set cran=FALSE I assume the snapshot tests should still run on CI, right? If we do eventually submit to CRAN we can't run most of these tests because CRAN won't have CmdStan installed and probably won't let us install it on CRAN systems just to run our tests. So we'd probably end up doing what RStudio does with their tensorflow package:

https://github.com/rstudio/tensorflow/blob/main/tests/testthat.R

[VisruthSK]

Ah yes, forgot about that. Will fix that in a bit.

[jgabry]

I think this is pretty much good to go. I made one small change request and suggested adding one code comment, but otherwise I've come around to the idea that switching to snapshots for these print tests is probably for the best, despite losing the explicitness of the assertions in the old tests.

[VisruthSK]

Yes the main thing now is that we need to be very protective of the snaps and ensure they aren't changed spuriously. If the API does change its a lot easier to update tests.

[jgabry]

Yes the main thing now is that we need to be very protective of the snaps and ensure they aren't changed spuriously.

Yeah definitely. We need to make sure no snapshot updates are snuck into large PRs without realizing it.