TST: Add more corner case coverage and remove unreachable

[bashtage]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 95.74468% with 2 lines in your changes missing coverage. Please review.

Project coverage is 98.67%. Comparing base (aeae819) to head (8805fa5).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
randomgen/tests/test_direct.py	90.90%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #390      +/-   ##
==========================================
+ Coverage   98.39%   98.67%   +0.27%     
==========================================
  Files          56       56              
  Lines        8643     8653      +10     
  Branches      642      653      +11     
==========================================
+ Hits         8504     8538      +34     
+ Misses        111       89      -22     
+ Partials       28       26       -2     

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