Use testing helpers

[pkqk]

• Make sure t.Helper() is called everywhere relevant
• Use t.Cleanup() to remove custom teardown code
• Move a setting change that was in a strange place to closer to the test function

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (0dc87b1) 71.06% compared to head (2618068) 71.06%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #219 +/- ## ======================================= Coverage 71.06% 71.06% ======================================= Files 27 27 Lines 2737 2737 ======================================= Hits 1945 1945 Misses 670 670 Partials 122 122 ```

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