add tests for rotation

[ismael-mendoza]

Unfortunately committed the rotation to develop directly rather than pushing it to a different branch 😅 . But this tests that it works

Closes #370

[codecov]

Codecov Report

Base: 89.55% // Head: 89.81% // Increases project coverage by +0.26% 🎉

Coverage data is based on head (4a7e414) compared to base (1d862ee).
Patch has no changes to coverable lines.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #383      +/-   ##
===========================================
+ Coverage    89.55%   89.81%   +0.26%     
===========================================
  Files           11       11              
  Lines         1522     1522              
===========================================
+ Hits          1363     1367       +4     
+ Misses         159      155       -4     

Flag	Coverage Δ
unittests	89.81% <ø> (+0.26%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
btk/draw_blends.py	91.43% <0.00%> (+1.55%)	⬆️

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