Recently, I noticed an odd behavior when running tests through make - every test failure causes my screen to flash. I'm using Ubuntu 18.04, and the kind of flash I get is the same as when you press the "print screen" button.
After doing various experiments, I've narrow it down to these two arguments passed to jtreg:

 -observerDir:/w/lt/panama/dev/build/linux-x86_64-server-release/images/test/failure_handler/jtregFailureHandler.jar -observer:jdk.test.failurehandler.jtreg.GatherDiagnosticInfoObserver

Without those the screen flashing does NOT occur.