Description

This PR adds tests for the vectors layer, improves the doc strings and cleans up the code a tiny bit, but doesn't change any functionality.

One question is - should the input parameters be
edge_width, edge_color, and length for the width, color, and the multiplicative length factor for the vectors or should they be something else. They used to just be width, color, and length but I added edge_ to make the parameters the same as for the points and shapes layer, though you could argue that for the points layer the parameters do different things and that in the vectors layer we don't have a face and an edge so it is just confusing. I'm open to suggestions - personally I like the consistency - but we can change it. Thoughts @bryantChhun @kevinyamauchi @jni?

Type of change

• Bug-fix (non-breaking change which fixes an issue)

How has this been tested?

• adds napari/layers/vectors/tests/test_vectors.py

Final checklist:

• My PR is the minimum possible work for the desired functionality
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works