simplify ScalaTest usage

[SethTisue]

ScalaTest was not fully published for RC1 (Scala.js artifacts were missing), so that's the reason to drop RC1. it's fine, we'd have dropped it soon anyway when adding RC3 dropped in #602

[SethTisue]

the Scala 2 jobs are now green

but presumably there's no way to make this PR mergeable until there's an upstream fix (in the ScalaTest repo) for this, as seen in the Scala-3-only failure:

[error] -- Error: /home/travis/build/playframework/play-json/play-json/shared/src/test/scala/play/api/libs/json/JsonSharedSpec.scala:137:32 
276[error] 137 |      "js.toJsObject(1)".mustNot(typeCheck)
277[error]     |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
278[error]     |      The 'mustNot typeCheck' syntax only works with String literals.
279[error]     | This location contains code that was inlined from JsonSharedSpec.scala:137

over at #594, @griggt said he'd look into it

[griggt]

In short, the ScalaTest typeCheck matcher is currently broken in Scala 3.

This appears to be known to the maintainers, because the entire test suite for this feature has been excluded in the Dotty build.

The immediate issue causing the confusing only works with String literals error seen above is that one of the macros contains obsolete/unmaintained code matching on the wrong tree shape: it is expecting an Apply node when what we have is a Literal(StringConstant(_)).

That is an easy fix, and making that change would allow the tests here to pass. However, the remainder of the current ScalaTest implementation does not conform to the documented semantics for the typeCheck matcher, namely that mustNot(typeCheck) should enforce that the code is free of syntax errors but fails type checking. Instead it would behave identically to mustNot(compile), where either parser or typer errors result in the test succeeding. There are some additional issues (with multiline string literals and stripMargin, etc.) that I will omit here for brevity.

Incidentally, the Scala 3 implementation of illTyped here has the same issue. Both implementations use the scala.compiletime.testing.typeChecks API, which returns false on any parser or typer errors.

Some options for this PR

1. Keep illTyped as-is (at least for now) but proceed with other changes
2. Wait for an upstream fix in ScalaTest
3. Use mustNot(compile) instead of mustNot(typeCheck)

Regardless of the decision taken here, I plan to work on a PR for ScalaTest to fix mustNot(typeCheck) in Scala 3.

[griggt]

Upstream PR: scalatest/scalatest#2008

[SethTisue]

current status: that PR is now merged, but there is no 3.2.9 yet; perhaps they're waiting for the next Scala 3 release (3.0.0-RC4 or 3.0.0 final)