Audit existing tests, get back to green, and add more tests

[drusepth]

Expected behavior

• Our test suite should be green.
  • After the test suite is green, we should lock the master branch and require all new contributions through green PRs.
• Test coverage should cover a larger percentage of the codebase.
• Tests should only fail for functional errors; not frontend/design changes.

Actual behavior

• Most tests are commented out, aren't quality tests, and/or extremely old and failing.
• New tests haven't been written in many years.

Steps to reproduce the behavior

Tests can be run with the command rake test:

drusepth@perseverance:~/Code/indentlabs/notebook$ rake test
RAILS_GROUPS is unset; defaulting to web,worker
Run options: --seed 63701

# Running:
[...failures...]
..................................................................................................................................

Finished in 37.916894s, 5.3011 runs/s, 17.7757 assertions/s.
201 runs, 674 assertions, 0 failures, 2 errors, 0 skips