@Test
    public void testDoubleAdd() {
        String drl =
                "import org.drools.compiler.xpath.*;\n" +
                "\n" +
                "rule R2 when\n" +
                "  Group( $id: name, $p: /members{age >= 20} )\n" +
                "then\n" +
                "  System.out.println( $id + \".\" + $p.getName() );\n" +
                "  insertLogical(      $id + \".\" + $p.getName() );\n" +
                "end\n";

        KieSession ksession = new KieHelper().addContent( drl, ResourceType.DRL )
                                             .build()
                                             .newKieSession();
        
        Group x = new Group("X");
        Group y = new Group("Y");
        ksession.insert( x );
        ksession.insert( y );
        ksession.fireAllRules();
        assertFalse (factsCollection(ksession).contains("X.Ada"));
        assertFalse (factsCollection(ksession).contains("X.Bea"));
        assertFalse (factsCollection(ksession).contains("Y.Ada"));
        assertFalse (factsCollection(ksession).contains("Y.Bea"));
        
        Adult ada = new Adult("Ada", 20);
        Adult bea = new Adult("Bea", 20);
        x.addPerson(ada);
        x.addPerson(bea);
        y.addPerson(ada);
        y.addPerson(bea);
        ksession.fireAllRules();
        assertTrue  (factsCollection(ksession).contains("X.Ada"));
        assertTrue  (factsCollection(ksession).contains("X.Bea"));
        assertTrue  (factsCollection(ksession).contains("Y.Ada"));
        assertTrue  (factsCollection(ksession).contains("Y.Bea"));
        
        x.removePerson(ada);
        x.removePerson(bea);
        y.removePerson(ada);
        y.removePerson(bea);  
        ksession.fireAllRules();
        assertFalse (factsCollection(ksession).contains("X.Ada"));
        assertFalse (factsCollection(ksession).contains("X.Bea"));
        assertFalse (factsCollection(ksession).contains("Y.Ada"));
        assertFalse (factsCollection(ksession).contains("Y.Bea"));
    }
    
    @Test
    public void testDoubleRemove() {
        String drl =
                "import org.drools.compiler.xpath.*;\n" +
                "\n" +
                "rule R2 when\n" +
                "  Group( $id: name, $p: /members{age >= 20} )\n" +
                "then\n" +
                "  System.out.println( $id + \".\" + $p.getName() );\n" +
                "  insertLogical(      $id + \".\" + $p.getName() );\n" +
                "end\n";

        KieSession ksession = new KieHelper().addContent( drl, ResourceType.DRL )
                                             .build()
                                             .newKieSession();
        
        Adult ada = new Adult("Ada", 20);
        Adult bea = new Adult("Bea", 20);
        Group x = new Group("X");
        Group y = new Group("Y");
        x.addPerson(ada);
        x.addPerson(bea);
        y.addPerson(ada);
        y.addPerson(bea);
        ksession.insert( x );
        ksession.insert( y );
        ksession.fireAllRules();
        assertTrue  (factsCollection(ksession).contains("X.Ada"));
        assertTrue  (factsCollection(ksession).contains("X.Bea"));
        assertTrue  (factsCollection(ksession).contains("Y.Ada"));
        assertTrue  (factsCollection(ksession).contains("Y.Bea"));
        
        x.removePerson(ada);
        x.removePerson(bea);
        y.removePerson(ada);
        y.removePerson(bea);  
        ksession.fireAllRules();
        assertFalse (factsCollection(ksession).contains("X.Ada"));
        assertFalse (factsCollection(ksession).contains("X.Bea"));
        assertFalse (factsCollection(ksession).contains("Y.Ada"));
        assertFalse (factsCollection(ksession).contains("Y.Bea"));
    }