Improve test coverage

[odow]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.63%. Comparing base (ee11833) to head (fca4690).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/visualization/value_functions.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #810      +/-   ##
==========================================
+ Coverage   93.59%   95.63%   +2.03%     
==========================================
  Files          26       26              
  Lines        3528     3527       -1     
==========================================
+ Hits         3302     3373      +71     
+ Misses        226      154      -72     

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