add tests

[joamatab]

@sebastian-goeldi
@SkandanC

TODO:

• fix MZI code and include test

[codecov]

Codecov Report

Merging #16 (c7f2285) into main (3097df0) will decrease coverage by 18.61%.
Report is 6 commits behind head on main.
The diff coverage is 86.89%.

❗ Current head c7f2285 differs from pull request most recent head 0fa6826. Consider uploading reports for the commit 0fa6826 to get more accurate results

@@             Coverage Diff             @@
##             main      #16       +/-   ##
===========================================
- Coverage   85.93%   67.32%   -18.61%     
===========================================
  Files          17       18        +1     
  Lines         661      606       -55     
===========================================
- Hits          568      408      -160     
- Misses         93      198      +105     

Files Changed	Coverage Δ
kgeneric/cells/straight.py	70.00% <0.00%> (ø)
kgeneric/cells/taper.py	100.00% <ø> (ø)
kgeneric/routing.py	45.45% <45.45%> (ø)
kgeneric/cells/mzi.py	20.77% <60.00%> (-59.49%)	⬇️
kgeneric/cells/bezier.py	81.08% <66.66%> (-0.50%)	⬇️
kgeneric/gpdk.py	87.50% <87.50%> (ø)
kgeneric/layers.py	88.33% <88.33%> (ø)
kgeneric/cells/grating_coupler_elliptical.py	91.66% <95.00%> (ø)
kgeneric/__init__.py	100.00% <100.00%> (ø)
kgeneric/cells/__init__.py	100.00% <100.00%> (ø)
... and 7 more

... and 1 file with indirect coverage changes

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