Add python tests

[mariekers]

Make sure python code works and isn't broken by changes

Dependent on #59

Not an expert but here's some tips on writing python tests

[themightychris]

I'd also consider this one done already given that you broke out #61 too -- that covers all that's left

(feel free to reopen with more detail if I'm misreading that)

[mariekers]

Adding unit tests to the functions within app.py

workflow in git actions does a build check - can we do tests on individual functions?

[themightychris]

A python workflow was already implemented into GitHub actions in #52:

• pytest gets run at the end of the pythonapp workflow: https://github.com/CodeForPhilly/chime/pull/52/files#diff-7e3bc64c9dd0eb02c0cac6101ee4e286R40
• test_app.py was created with a single sample assertion: https://github.com/CodeForPhilly/chime/pull/52/files#diff-dda76c240c44e9a17f6534f1a4065235R4

The TODO at this point is just to actually add meaningful tests to test_app.py. What are some examples of function this issue might cover testing that would not be part of #61?

I just updated the testing section of the docs: https://codeforphilly.github.io/chime/contributing/app-dev.html#testing

[themightychris]

Over here you can see how even though the current test_app.py only has one trivial assertion, that alone covers a lot of ground in at least ensuring the application and its deps can be loaded: https://github.com/CodeForPhilly/chime/pull/55/checks?check_run_id=515843837

[garysieling]

I thought about this a bit, here what I would propose - this should be a pretty straightforward task for someone who knows python reasonably well.

1. Make a test that takes runs using inputs that you can pick in the UI - assert that the model produces the same results currently. Do something like 50 randomized selections of the current inputs. This would prevent regressions.

2. Test each input to the model for edge cases (what happens if I put in 0, a really large number, a fraction, if there are any of those)

3. Track down the original paper for this model and write a test that replicate their results

[garysieling]

Possible that I've duplicated the intent of issue #61 in the above

[pjhoberman]

I'm going to attempt some tests here, and see if the charting functions return values so that those can be tested (since I have no idea how to make Python look at an actual visual and see if it worked...).

Question: Would you rather this be part of the github actions, or part of the developer flow (git hooks) so that devs can't even push a change without running and passing a test?

[themightychris]

@pjhoberman we already have pytest gating pull requests, so my sense is we should just start with adding tests to test_app.py

I don't think we need to mess with running it via githooks right now, devs being able to run pytest and then GitHub running that against PRs should be a great start