Feat/add mutation testing

[nathanrpage97]

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• I accept that @willmcgugan may be pedantic in the code review.

Description

Please describe your changes here. If this fixes a bug, please link to the issue, if possible.

[codecov-io]

Codecov Report

Merging #3 (f17d6d7) into master (31ceb88) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #3   +/-   ##
=======================================
  Coverage   99.72%   99.72%           
=======================================
  Files          55       55           
  Lines        4812     4812           
=======================================
  Hits         4799     4799           
  Misses         13       13           

Flag	Coverage Δ
unittests	99.72% <ø> (ø)

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[github-actions]

Unit Test Results

    2 files      2 suites   9s ⏱️
410 tests 410 ✔️ 0 💤   0 ❌
473 runs  461 ✔️ 0 💤 12 ❌

Results for commit f17d6d7.