The background for this is what happened a few months back when we had tests that required a new feature (CODETOOLS-7900178) in jtreg, but people had not updated their local copy. This resulted in a number of false bug reports and unnecessary email traffic. In that particular case, it was not obvious that the solution was to update jtreg. If instead there had been a clear error message saying that jtreg needed updating, we would have saved lots of time.