Expanded selector tests

[marcus7070]

The selector tests haven't been updated in a while, before I work on #517 I wanted to expand them a bit and help me catch any mistakes I make while refactoring some selectors.

I also removed that "polygon with rounded corners" test from testRadiusNthSelector, that's an edge case at best and not something we should be testing for.

[codecov]

Codecov Report

Merging #541 (de2cef9) into master (a03648c) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #541      +/-   ##
==========================================
+ Coverage   94.11%   94.14%   +0.03%     
==========================================
  Files          29       29              
  Lines        6185     6204      +19     
  Branches      655      663       +8     
==========================================
+ Hits         5821     5841      +20     
  Misses        225      225              
+ Partials      139      138       -1     

Impacted Files	Coverage Δ
tests/test_selectors.py	100.00% <100.00%> (ø)
cadquery/cq.py	89.45% <0.00%> (+0.10%)	⬆️

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[marcus7070]

This is ready to review and/or merge.

[jmwright]

@marcus7070 Thanks!