Convert system_test, test_abf, test_basic_maths to PyTest

[trexfeathers]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.95%. Comparing base (03c21c8) to head (f1c21d8).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6604   +/-   ##
=======================================
  Coverage   89.95%   89.95%           
=======================================
  Files          91       91           
  Lines       24447    24447           
  Branches     4567     4567           
=======================================
  Hits        21992    21992           
  Misses       1686     1686           
  Partials      769      769           

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