A few times when I viewed the test execution, i saw that a couple of tests produce some UI artifacts, which may or may not cause the test to fail. The artifacts are intermittent and usually do not appeared on test rerun.

But here are a few ways to reproduce them(artifacts are black or red random rectangles on the frame).

1. Run the ./netbeans/bin/netbeans -J-Dsun.java2d.metal=true --jdkhome .../jdk
   Make the netbeans window as small as possible
   Double click the title(do not use the green/zoom button) See that maximization animation is not smooth and produces red or black artifacts.

2. The test/jdk/java/awt/Frame/MaximizedToOppositeScreen/" can be used to reproduce the artifacts(but the tests will pass)

Both cases above work fine if the opengl is in use.