When running the tooling test cases on a server box, you may encounter the following exception:
java.lang.NoClassDefFoundError: sun/awt/X11GraphicsEnvironment
This is not actually due to a missing class, but to the fact that certain graphics operations on these system need access to the Xserver. To overcome this issue, you need to set the DISPLAY variable to an accessible Xserver: export DISPLAY=hostname:0 in bash, for example. Make sure you can actually connect to that Xserver, e.g., by starting an xterm. The easiest way to ensure this works is by connecting to the server via X11 in the first place, then these issues should not arise.
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