Improved OTS Tests

[ccoffrin]

Add checks for the number of active branches in OTS solutions.

[codecov]

Codecov Report

Merging #718 into master will decrease coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #718      +/-   ##
==========================================
- Coverage   92.80%   92.76%   -0.05%     
==========================================
  Files          42       42              
  Lines        7506     7570      +64     
==========================================
+ Hits         6966     7022      +56     
- Misses        540      548       +8     

Impacted Files	Coverage Δ
src/core/objective.jl	88.27% <0.00%> (-0.22%)	⬇️

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