Refactor and type non-permission tests

[florimondmanca]

Refs #102 (comment), refs #89.

[codecov-io]

Codecov Report

Merging #109 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #109      +/-   ##
==========================================
- Coverage   96.39%   96.37%   -0.02%     
==========================================
  Files          22       22              
  Lines         471      469       -2     
==========================================
- Hits          454      452       -2     
  Misses         17       17

Impacted Files	Coverage Δ
tests/test_checks.py	100% <100%> (ø)	⬆️
tests/test_legacy_key_generator.py	100% <100%> (ø)	⬆️

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