Java testkit now uses effectiveUri to behave just like the Scala testkit so that
the host header and path is joined. This allows for test calls that use just a relative
URI.
- explicitly provide Unit values and place parens around tuple creation
- remove structural type usage in TestUtils
- fix Java double-casts
- use unused Java values by asserting their non-nullness
- work around inability to place case class in trait (scripted test)
The remaining warnings about using private types in public methods are
bogus as reported in https://issues.scala-lang.org/browse/SI-9490.
