To reproduce this:

$ gradle --info :web:test

You will get the following exception and the test build will hang:

javafx.scene.web.DOMTest > testDOMWindowAndStyleAccess STANDARD_ERROR
    java.lang.NullPointerException
        at com.sun.javafx.Utils.getScreen(Utils.java:686)
        at com.sun.javafx.webkit.WebPageClientImpl.getScreenBounds(WebPageClientImpl.java:105)
        at com.sun.webkit.WCWidget.fwkGetScreenRect(WCWidget.java:118)
        at com.sun.webkit.dom.DOMWindowImpl.resizeByImpl(Native Method)
        at com.sun.webkit.dom.DOMWindowImpl.resizeBy(DOMWindowImpl.java:1151)
        at javafx.scene.web.DOMTest.lambda$testDOMWindowAndStyleAccess$49(DOMTest.java:344)
        at javafx.scene.web.DOMTest$$Lambda$239/6426732.run(Unknown Source)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)
        at com.sun.javafx.application.PlatformImpl.lambda$null$169(PlatformImpl.java:295)
        at com.sun.javafx.application.PlatformImpl$$Lambda$49/7248969.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at com.sun.javafx.application.PlatformImpl.lambda$runLater$170(PlatformImpl.java:294)
        at com.sun.javafx.application.PlatformImpl$$Lambda$48/33309185.run(Unknown Source)
        at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
        at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
        at com.sun.glass.ui.win.WinApplication.lambda$null$144(WinApplication.java:101)
        at com.sun.glass.ui.win.WinApplication$$Lambda$37/11339419.run(Unknown Source)
        at java.lang.Thread.run(Thread.java:744)
> Building > :web:test > 289 tests completed, 7 skipped