Support ScalaTest printing inside TestBuilder

[seldridge]

There are a lot of useful printing features inside ScalaTest that are currently not usable inside a TestBuilder environment:

• Given/When/Then of GivenWhenThen
• info of Informing
• feature/scenario of FeatureSpec variants

This limits the ability of a user to write a descriptive test that provides ScalaTest-reported output about what the test is doing. Users can always rely on println (which does work). However, println isn't integrated with the ScalaTest environment in any way and doesn't expose at what point in a test something failed.

As one example, I'd like the following to be supported:

behavior of "Foo"

it should "bar" in {
  def test(new Foo) { c => 
    Given("a Foo initialized via reset for 4 cycles")
    c.doReset(4)

    When("a sequence is enqueued")
    c.in.enqueSeq(Seq(1, 2, 3))

    Then("the same sequence should be dequeued")
    c.out.expectDequeueSeq(Seq(1, 2, 3))
  }
}

Currently, this will just swallow the Given/When/Then and not print them.

See: http://doc.scalatest.org/3.1.0/org/scalatest/GivenWhenThen.html

This is related to some comments I made in #68, but is really a disjoint issue.

[ekiwi]

Tighter scalatest integration is something that probably won't happen.