> Let me ask your own question back at you: what's there to understand with WordSpec or Cucumber-style tests?
To use Cucumber you have to understand a whole new grammar. To use ScalaTest you have to understand relatively obscure parts of Scala (implicit conversions, "word word word" style method calls, by-name parameters, ...) - or else treat it like a config file and learn a whole new grammar. To use JUnit you just write plain old Java/Scala.
Yes, when a WordSpec test starts failing, junior devs know how to fix it without my assistance. I haven't noticed any difference in dev effectiveness between ScalaTest and JUnit.