Port of #447 for Cats

[fthomas]

This is a port of #447 for Cats. One reason for doing this is to see if the 2.10 build fails in a similar way.

/cc @fommil

[fommil]

Damn.

How do you want to do the 2.11+ restriction? I'm not sure how to do that in your codebase.

[fthomas]

The first commit in this PR failed on all Scala versions with:

[error] /home/travis/build/fthomas/refined/modules/cats/shared/src/test/scala/eu/timepit/refined/cats/RefTypeMonadErrorSpec.scala:78:26: diverging implicit expansion for type eu.timepit.refined.api.RefType[F]
[error] starting with method refTypeMonadError in package cats
[error]     val decoder = Decoder[PosInt]
[error]                          ^

Commenting out a seemingly unrelated test in bdc0b26 fixed the 2.11+ builds while the 2.10 build still fails with that error.

[codecov]

Codecov Report

Merging #449 into master will decrease coverage by 1.26%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #449      +/-   ##
==========================================
- Coverage   98.01%   96.75%   -1.27%     
==========================================
  Files          57       57              
  Lines         655      677      +22     
  Branches       12       12              
==========================================
+ Hits          642      655      +13     
- Misses         13       22       +9

Impacted Files	Coverage Δ
...c/main/scala/eu/timepit/refined/cats/package.scala	100% <100%> (ø)	⬆️
...main/scala/eu/timepit/refined/scalaz/package.scala	100% <0%> (ø)	⬆️

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[fthomas]

@fommil The easiest option to make #447 2.11+ only would be to not run the tests with 2.10. In this PR I choose to run the test for refTypeMonadError only with 2.12. It would be great if the build would support scala-2.11+ source directories but this is not the case right now. So until scala-2.11+ directories are supported or 2.10 support is dropped I'm fine with testing that instance only with 2.12.

[fommil]

Ok great, but the addition of the implicit is breaking one of the existing tests in a way I don't understand.

[fthomas]

I'm also okay with not running RefTypeSpecScalazTag with 2.10 and making it 2.12 only.

[fommil]

great! So how do we do that from a practical point of view? I'm not sure how to disable a test.

[fthomas]

Moving the test file from refined/modules/scalaz/shared/src/test/scala/eu/timepit/refined/scalaz/ to refined/modules/scalaz/shared/src/test/scala-2.12/eu/timepit/refined/scalaz/ does the trick.

[fommil]

Will you cut a release soon with these new things?

[fthomas]

I'll want to process some of the open PRs and need to update the release notes before cutting the next release. That will probably take me one or two weeks.