on linux when a display is not connected (read reported as connected by xrandr), a number of JCK tests that utilize java.awt.GraphicsDevice.get/setDisplayMode fail.

The tests that fail are:

api/java_awt/GraphicsDevice/indexTGF.html#General[getDisplayMode_nonNull]
api/java_awt/GraphicsDevice/indexTGF.html#SetDisplayModeExceptions[IAE_nonExistingDisplayMode]
api/java_awt/GraphicsDevice/indexTGF.html#SetDisplayModeExceptions[IAE_nullDisplayMode]
api/java_awt/GraphicsDevice/indexTGF.html#SetGetFullScreenWindow[getSetWindow]
api/java_awt/GraphicsDevice/indexTGF.html#SetGetFullScreenWindow[getSet_Null]
api/java_awt/GraphicsDevice/indexTGF.html#SetGetFullScreenWindow[setFullScreenWindow_visibleAfterReturning]
api/java_awt/SplashScreen/AnimatedContentTests.html#AnimatedContentTests[testAnimation]
api/java_awt/SplashScreen/AnimatedContentTests.html#AnimatedContentTests[testDefaultPosition]
api/java_awt/SplashScreen/AnimatedContentTests.html#AnimatedContentTests[testWindowBounds]
api/java_awt/SplashScreen/AnimatedContentTests.html#AnimatedContentTests[testWindowSize]
api/java_awt/SplashScreen/CreateGraphicsTestsOpq.html#CreateGraphicsTestsOpq[testDrawingOverSplashScreen]
api/java_awt/SplashScreen/SetImageURLTestsImage.html#SetImageURLTestsImage[testWindowReposition]
api/java_awt/SplashScreen/SetImageURLTestsImage.html#SetImageURLTestsImage[testWindowResize]
api/java_awt/SplashScreen/SetImageURLTestsJar.html#SetImageURLTestsJar[testWindowReposition]
api/java_awt/SplashScreen/SetImageURLTestsJar.html#SetImageURLTestsJar[testWindowResize]
api/java_awt/SplashScreen/TransparencyTestsArgGIF.html#TransparencyTestsArgGIF[testTransparency]
api/java_awt/SplashScreen/TransparencyTestsMnfPNG.html#TransparencyTestsMnfPNG[testTransparency]
api/java_awt/SplashScreen/TransparentContentTestsArgGIF.html#TransparentContentTestsArgGIF[testDefaultPosition]
api/java_awt/SplashScreen/TransparentContentTestsArgGIF.html#TransparentContentTestsArgGIF[testWindowBounds]
api/java_awt/SplashScreen/TransparentContentTestsArgGIF.html#TransparentContentTestsArgGIF[testWindowSize]
api/java_awt/SplashScreen/TransparentContentTestsMnfPNG.html#TransparentContentTestsMnfPNG[testDefaultPosition]
api/java_awt/SplashScreen/TransparentContentTestsMnfPNG.html#TransparentContentTestsMnfPNG[testWindowBounds]
api/java_awt/SplashScreen/TransparentContentTestsMnfPNG.html#TransparentContentTestsMnfPNG[testWindowSize]
api/java_awt/Window/indexTGF.html#BackgroundGeneral[testNoAlphaFullScreen]
api/java_awt/Window/indexTGF.html#ShapeExceptions[testICSEThrowing_fullScreen]
api/java_awt/Window/indexTGF.html#ShapeGeneral[nullShapeForFullScreen]
api/java_awt/GraphicsDevice/indexTGF.html#ShapeAndTranslucencyForFullScreen[nullShape]
api/java_awt/GraphicsDevice/indexTGF.html#ShapeAndTranslucencyForFullScreen[opacityReset]
api/java_awt/SplashScreen/SetImageURLTestsImage.html#SetImageURLTestsImage[testImage]
api/java_awt/SplashScreen/SetImageURLTestsJar.html#SetImageURLTestsJar[testImage]
api/java_awt/SplashScreen/StaticContentTestsArgGIF.html#StaticContentTestsArgGIF[testDefaultPosition]
api/java_awt/SplashScreen/StaticContentTestsArgGIF.html#StaticContentTestsArgGIF[testWindowBounds]
api/java_awt/SplashScreen/StaticContentTestsArgGIF.html#StaticContentTestsArgGIF[testWindowSize]
api/java_awt/SplashScreen/StaticContentTestsArgJPG.html#StaticContentTestsArgJPG[testDefaultPosition]
api/java_awt/SplashScreen/StaticContentTestsArgJPG.html#StaticContentTestsArgJPG[testWindowBounds]
api/java_awt/SplashScreen/StaticContentTestsArgJPG.html#StaticContentTestsArgJPG[testWindowSize]
api/java_awt/SplashScreen/StaticContentTestsArgPNG.html#StaticContentTestsArgPNG[testDefaultPosition]
api/java_awt/SplashScreen/StaticContentTestsArgPNG.html#StaticContentTestsArgPNG[testWindowBounds]
api/java_awt/SplashScreen/StaticContentTestsArgPNG.html#StaticContentTestsArgPNG[testWindowSize]
api/java_awt/SplashScreen/StaticContentTestsMnfGIF.html#StaticContentTestsMnfGIF[testDefaultPosition]
api/java_awt/SplashScreen/StaticContentTestsMnfGIF.html#StaticContentTestsMnfGIF[testWindowBounds]
api/java_awt/SplashScreen/StaticContentTestsMnfGIF.html#StaticContentTestsMnfGIF[testWindowSize]
api/java_awt/SplashScreen/StaticContentTestsMnfJPG.html#StaticContentTestsMnfJPG[testDefaultPosition]
api/java_awt/SplashScreen/StaticContentTestsMnfJPG.html#StaticContentTestsMnfJPG[testWindowBounds]
api/java_awt/SplashScreen/StaticContentTestsMnfJPG.html#StaticContentTestsMnfJPG[testWindowSize]
api/java_awt/SplashScreen/StaticContentTestsMnfPNG.html#StaticContentTestsMnfPNG[testDefaultPosition]
api/java_awt/SplashScreen/StaticContentTestsMnfPNG.html#StaticContentTestsMnfPNG[testWindowBounds]
api/java_awt/SplashScreen/StaticContentTestsMnfPNG.html#StaticContentTestsMnfPNG[testWindowSize]
api/java_awt/GraphicsDevice/indexTGF.html#SetFullScreenWindowExclusive[coversAllScreenDevice]
api/java_awt/GraphicsDevice/indexTGF.html#SetFullScreenWindowExclusive[thereCouldBeOnlyOne]
api/java_awt/SplashScreen/CreateGraphicsTestsTsp.html#CreateGraphicsTestsTsp[testDrawingOverSplashScreen]
api/java_awt/SplashScreen/StaticContentTestsArgGIF.html#StaticContentTestsArgGIF[testImage]
api/java_awt/SplashScreen/StaticContentTestsArgJPG.html#StaticContentTestsArgJPG[testImage]
api/java_awt/SplashScreen/StaticContentTestsArgPNG.html#StaticContentTestsArgPNG[testImage]
api/java_awt/SplashScreen/StaticContentTestsMnfGIF.html#StaticContentTestsMnfGIF[testImage]
api/java_awt/SplashScreen/StaticContentTestsMnfJPG.html#StaticContentTestsMnfJPG[testImage]
api/java_awt/SplashScreen/StaticContentTestsMnfPNG.html#StaticContentTestsMnfPNG[testImage]
api/java_awt/SplashScreen/index.html#PrecedenceTest[testImageIsCorrect]

the reason for the failure is that GraphicsDevice.getDisplayMode() returns null in such case, and GraphicsDevice.setDisplayMode() throws NPE.