Add tests for acl selectors with no permissions or patterns

[madolson]

I prefer the assert_blah style since it gives a precise line number instead of the end of the test. The wording was also wrong, %RW~ does something, it gives access to the single empty key, so updated the wording.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.85%. Comparing base (c0014ef) to head (bf94455).
Report is 3 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1515      +/-   ##
============================================
+ Coverage     70.82%   70.85%   +0.03%     
============================================
  Files           120      120              
  Lines         64911    64914       +3     
============================================
+ Hits          45972    45994      +22     
+ Misses        18939    18920      -19     

see 12 files with indirect coverage changes