[WIP] enhance unit testing

[ChristianBeer]

Some simple enhancements to unit testing. Still WIP.

Description of the Change
More unit testing of library functions.

Alternate Designs
Alternatively one could add the reference files to git and copy them into the directory where tests are executed but that seemed more work than reading and writing directly from within the test.

Release Notes
N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 11.16%. Comparing base (6f8fba3) to head (8275531).
⚠️ Report is 4151 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4597      +/-   ##
============================================
+ Coverage     10.90%   11.16%   +0.25%     
  Complexity     1044     1044              
============================================
  Files           277      277              
  Lines         35626    35627       +1     
  Branches       7852     7852              
============================================
+ Hits           3886     3976      +90     
+ Misses        31520    31431      -89     
  Partials        220      220              

see 9 files with indirect coverage changes

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