Certain client tests access fields and methods of internal classes using setAccessible(true). After recent encapsulation changes in Jigsaw code this would often require explicit export of the internal class to the test. One of the simple examples is com/sun/java/swing/plaf/windows/WindowsRadioButtonUI/7089914/bug7089914.java test.
To pass now, it needs @requires os.family == "windows" tag and @modules java.desktop/com.sun.java.swing.plaf.windows export tag.

More complex case is that of helpers handling several OS-specific classes in several clauses of one if-then-else statement. To fix that we need more profound change and another bug.

Tentative list of the tests to fix:
java/awt/Modal/LWModalTest/LWModalTest.java
java/awt/TextArea/TextAreaCaretVisibilityTest/bug7129742.java
com/sun/java/swing/plaf/windows/WindowsRadioButtonUI/7089914/bug7089914.java
    java/awt/image/MultiResolutionImageTest.java (has a multisystem par, so removed from this list)
java/awt/WMSpecificTests/Metacity/FullscreenDialogModality.java
java/awt/WMSpecificTests/Mutter/MutterMaximizeTest.java