Unit test `sdr.plot` subpackage

[mhostetter]

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.87%. Comparing base (e0e4e7b) to head (2f33e20).

Additional details and impacted files

@@                Coverage Diff                @@
##           release/0.0.x     #450      +/-   ##
=================================================
+ Coverage          81.75%   81.87%   +0.12%     
=================================================
  Files                 63       63              
  Lines               3951     3951              
=================================================
+ Hits                3230     3235       +5     
+ Misses               721      716       -5     

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