lint: unit test improvements

[NathanBaulch]

Various unit test improvements that weren't caught by the recent introduction of the testifylint linter, discovered during my work on #672. Each commit addresses a different issue. These can be squash merged in their entirety or I can create more specific individual PRs if preferred.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.49%. Comparing base (3bc887c) to head (52f618b).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #674   +/-   ##
=======================================
  Coverage   94.49%   94.49%           
=======================================
  Files          18       18           
  Lines        3305     3305           
=======================================
  Hits         3123     3123           
  Misses        170      170           
  Partials       12       12           

Flag	Coverage Δ
unittests	94.49% <ø> (ø)

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