Improve specs

[rider-yi]

Added some tests for refined types

[codecov]

Codecov Report

Merging #493 into master will decrease coverage by 0.29%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #493     +/-   ##
=========================================
- Coverage   94.26%   93.97%   -0.3%     
=========================================
  Files          62       62             
  Lines         680      680             
  Branches       10       10             
=========================================
- Hits          641      639      -2     
- Misses         39       41      +2

Impacted Files	Coverage Δ
.../scala/eu/timepit/refined/api/RefinedTypeOps.scala	80% <0%> (-20%)	⬇️
...ain/scala/eu/timepit/refined/api/RefinedType.scala	88.88% <0%> (-11.12%)	⬇️

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[kusamakura]

I think as in #497 (comment), just test the from method. That should cut down on most of the copy paste work :)

[rider-yi]

Done

[fthomas]

LGTM, many thanks @rider-yi!