Clean up unit tests for engine

[JPercival]

• No functional changes
• Cleans up a bunch of unit tests to make them more readable

[github-actions]

Formatting check succeeded!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.90%. Comparing base (483122f) to head (9334bb0).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1340   +/-   ##
=========================================
  Coverage     62.89%   62.90%           
- Complexity     6108     6110    +2     
=========================================
  Files           468      468           
  Lines         25354    25354           
  Branches       4719     4719           
=========================================
+ Hits          15946    15948    +2     
+ Misses         7271     7269    -2     
  Partials       2137     2137           

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