The following test failed in the JDK21 CI:

java/awt/Graphics/GetGraphicsTest.java

Here's a snippet from the linux-aarch64 log file:

#section:main
----------messages:(7/269)----------
command: main GetGraphicsTest
reason: User specified action: run main GetGraphicsTest
started: Tue Apr 25 11:54:12 UTC 2023
Mode: othervm
Additional options from @modules: --add-modules java.desktop
finished: Tue Apr 25 11:54:12 UTC 2023
elapsed time (seconds): 0.455
----------configuration:(3/40)----------
Boot Layer
  add modules: java.desktop

----------System.out:(0/0)----------
----------System.err:(24/1267)----------
java.awt.HeadlessException:
No X11 DISPLAY variable was set,
or no headful library support was found,
but this program performed an operation which requires it,

at java.desktop/java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:166)
at java.desktop/java.awt.Window.<init>(Window.java:553)
at java.desktop/java.awt.Frame.<init>(Frame.java:428)
at java.desktop/java.awt.Frame.<init>(Frame.java:393)
at GetGraphicsTest.<init>(GetGraphicsTest.java:35)
at GetGraphicsTest.main(GetGraphicsTest.java:47)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:578)
at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
at java.base/java.lang.Thread.run(Thread.java:1592)

JavaTest Message: Test threw exception: java.awt.HeadlessException:
No X11 DISPLAY variable was set,
or no headful library support was found,
but this program performed an operation which requires it,

JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.awt.HeadlessException: No X11 DISPLAY variable was set, or no headful library support was found, but this program performed an operation which requires it,
----------rerun:(37/5400)*----------

The macosx-x64 log is even more on point:

#section:main
----------messages:(7/269)----------
command: main GetGraphicsTest
reason: User specified action: run main GetGraphicsTest
started: Tue Apr 25 12:04:57 GMT 2023
Mode: othervm
Additional options from @modules: --add-modules java.desktop
finished: Tue Apr 25 12:04:58 GMT 2023
elapsed time (seconds): 0.278
----------configuration:(3/40)----------
Boot Layer
  add modules: java.desktop

----------System.out:(0/0)----------
----------System.err:(20/1202)----------
java.awt.HeadlessException:
The application is not running in a desktop session,
but this program performed an operation which requires it.
at java.desktop/java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:166)
at java.desktop/java.awt.Window.<init>(Window.java:553)
at java.desktop/java.awt.Frame.<init>(Frame.java:428)
at java.desktop/java.awt.Frame.<init>(Frame.java:393)
at GetGraphicsTest.<init>(GetGraphicsTest.java:35)
at GetGraphicsTest.main(GetGraphicsTest.java:47)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:578)
at com.sun.javatest.regtest.agent.MainWrapper$MainTask.run(MainWrapper.java:138)
at java.base/java.lang.Thread.run(Thread.java:1592)

JavaTest Message: Test threw exception: java.awt.HeadlessException:
The application is not running in a desktop session,
but this program performed an operation which requires it.
JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.awt.HeadlessException: The application is not running in a desktop session, but this program performed an operation which requires it.
----------rerun:(36/5647)*----------