Improve test coverage

[odow]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 96.28%. Comparing base (0c99d6e) to head (d19fc08).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/visualization/spaghetti_plot.jl	50.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #811       +/-   ##
===========================================
+ Coverage        0   96.28%   +96.28%     
===========================================
  Files           0       26       +26     
  Lines           0     3523     +3523     
===========================================
+ Hits            0     3392     +3392     
- Misses          0      131      +131     

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