Unit test for everest constraints plot

[eilskra]

Issue
Resolves #13597

Approach
💭🧪📈
🤔

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.09%. Comparing base (e7fc16b) to head (6c5bf40).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13704      +/-   ##
==========================================
+ Coverage   89.94%   90.09%   +0.15%     
==========================================
  Files         468      468              
  Lines       33402    33411       +9     
==========================================
+ Hits        30043    30103      +60     
+ Misses       3359     3308      -51     

Flag	Coverage Δ
cli-tests	35.79% <ø> (-0.01%)	⬇️
fuzz	43.38% <ø> (-0.01%)	⬇️
gui-tests	59.27% <ø> (-0.01%)	⬇️
performance-and-unit-tests	77.82% <ø> (-0.03%)	⬇️
test	46.08% <ø> (+0.17%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.
see 7 files with indirect coverage changes

[codspeed-hq]

Merging this PR will not alter performance

✅ 36 untouched benchmarks

---

_{Comparing eilskra:constraint-plot-test (6c5bf40) with main (cbe09cc)}

[eqbech]

LGTM 💯