Migrate tests over to 'shared' so they run on Scala.js

[jdegoes]

A bunch of test suites right now run only on the JVM. As many as possible should be migrated over to shared so they run in Scala.js configuration.

The tests are currently located in core/jvm/src/test/scala/scalaz/zio and could be moved (one by one, PR by PR) to core/shared/src/test/scala/scalaz/zio.

• ArbitraryCause.scala
• ExitSpec.scala
• FiberLocalSpec.scala
• FiberSpec.scala
• FunctionIOSpec.scala
• GenIO.scala
• IOSpec.scala
• IOSyntaxSpec.scala
• PlatformSpec.scala
• PromiseSpec.scala
• QueueSpec.scala
• RefMSpec.scala
• RefSpec.scala
• RetrySpec.scala
• stm/STMSpec.scala
• duration/DurationSpec.scala
• duration/DurationSyntaxSpec.scala

Some of these may reveal bugs in Scala.js support that can then be fixed separately.

If anyone has interest in giving a hand here, just reply to this thread and pick out one of the test suites to migrate over (some will be quite simple).

[kamilkloch]

TestRuntime.scala uses TerminationMatchers from specs2. TerminationMatchers cannot be used in Scala.js (reference to Thread.sleep). Any ideas?

[LGLO]

Not every test requires TerminationMatchers, so we could split TestRuntime and put restricted version to shared.
Quick test: PromiseSpec and RefSpec pass tests. RefMSpec errors on tests of update and modify.

[vilu]

Is anyone actively working on this one? If not I would give it or a part of it a go late next week.

[LGLO]

@vilu this issue can be split to many small PRs.

[mgibowski]

I take two easy ones for the start: ArbitraryCause.scala and GenIO.scala.
The migration is so simple that I will put it into one PR.

[mgibowski]

If anybody is interested in stm/STMSpec.scala, take a look at this first: #803

[mgibowski]

Today I migrate RefSpec.scala and FunctionIOSpec.scala.

[LGLO]

My idea for some other tests is to replace runSync, which is disallowed in JS, with unsafeRunToFuture, so tests return Future[MatchResult[T]]. Then we can use specs2 Around that uses java.util.Timer and scala.concurrent.Promise to create Future with timeout.
WDYT guys?

[LGLO]

We can't block for result in scala-js, scalacheck is 100% synchronous on the other hand.
forAll tests will be challenging. Doable but I think we'll have to write quite a chunk of code to cover forAll.

[vilu]

I was looking into PlatformSpec, should this one be really be considered in this ticket seeing how the implementation differs between js/jvm? Maybe just removing this one from the list would make sense?