All these thests fail similarly on Ubuntu 17.10 with JDK 10.
Thess tests fail only on Ubuntu 17.10 and Not reproducible on Ubuntu 16.04
java/awt/Modal/ToBack/ToBackModeless1Test.java: Check whether a modeless dialog having a null Frame constructor goes behind other windows when toBack is called for it.
java/awt/Modal/ToBack/ToBackModeless2Test.java: Check whether a modeless dialog having a null Dialog constructor goes behind other windows when toBack is called for it.
java/awt/Modal/ToBack/ToBackModeless3Test.java: Check whether a modeless dialog having a hidden Frame constructor goes behind other windows when toBack is called for it.
java/awt/Modal/ToBack/ToBackModeless4Test.java: Check whether a modeless dialog having a hidden Dialog constructor goes behind other windows when toBack is called for it.
java/awt/Modal/ToBack/ToBackNonModal1Test.java: Check whether a non-modal dialog having a null Frame constructor goes behind other windows when toBack is called for it.
java/awt/Modal/ToBack/ToBackNonModal2Test.java: Check whether a non-modal dialog having a null Dialog constructor goes behind other windows when toBack is called for it.
java/awt/Modal/ToBack/ToBackNonModal3Test.java: Check whether a non-modal dialog having a hidden Frame constructor goes behind other windows when toBack is called for it.
java/awt/Modal/ToBack/ToBackNonModal4Test.java: Check whether a non-modal dialog having a hidden Dialog constructor goes behind other windows when toBack is called for it.