### Question:
DefaultTreeItemWithUniqueIDFactory extends
                                                AbstractTreeItemWithUniqueIDFactory <KEYTYPE, DATATYPE, DefaultTreeItemWithID <KEYTYPE, DATATYPE>> { @Nonnull public DefaultTreeItemWithID <KEYTYPE, DATATYPE> createRoot () { return new DefaultTreeItemWithID <> (this); }  @Nonnull DefaultTreeItemWithID <KEYTYPE, DATATYPE> createRoot();  }### Answer:
@Test public void testUniqueness () { final DefaultTreeItemWithUniqueIDFactory <String, String> x = new DefaultTreeItemWithUniqueIDFactory <> (); CommonsTestHelper.testDefaultImplementationWithEqualContentObject (x, new DefaultTreeItemWithUniqueIDFactory <String, String> ()); x.create (x.createRoot (), "any"); CommonsTestHelper.testDefaultImplementationWithDifferentContentObject (x, new DefaultTreeItemWithUniqueIDFactory <String, String> ()); }