Improve test coverage for zeros

[timholy]

xref #15

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.87%. Comparing base (ee03f45) to head (38ea407).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #16   +/-   ##
=======================================
  Coverage   92.87%   92.87%           
=======================================
  Files           5        5           
  Lines         856      856           
=======================================
  Hits          795      795           
  Misses         61       61           

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