assertFalse( children.retainAll( otherSet ) );
assertFalse( children.isDirty() );
otherSet = new HashSet();
otherSet.add( otherChild );
assertFalse( children.removeAll( otherSet ) );
assertFalse( children.isDirty() );
assertTrue( children.retainAll( otherSet ));
assertTrue( children.isDirty() );
assertTrue( children.isEmpty() );