Allow a custom function to name a test

[jschneidereit]

Right now we allow users to append tags to tests names, which is fine - but it would be even better to provide users an extension point to modify the name of the tests based on the test itself and tags (and perhaps other information).

Given a test with tags Slow and NickNack

status quo:

TestClass.nicknack does some stuff[tags = Slow, NickNack]

new hotness, in kotlin pseudocode:

val Slow = Tag("Slow")

val testNamer = object : TestNameExtension {
  override fun nameTest(testCase: TestCase, tags: Set<Tag>): String {
    if (tags.contains(Slow)) {
      return "Slow: ${testCase.name} [tags=${(tags - Slow).joinToString()}]"
   }
   return testCase.name

would give us a nice test name like

Slow: TestClass.nicknack does some stuff [tags = NickNack]