@Test
 public void constructorAllOK() throws XPathExpressionException {
   Variable[] vars = new Variable[2];
   vars[0] = new Variable("FOO", "//foo");
   vars[1] = new Variable("BAR", "//bar");
   SubscriptionProperties p = new SubscriptionProperties("//foo/bar", "node", vars);
   assertEquals("node", p.getNode());
   assertEquals("//foo/bar", p.getFilter());
   assertEquals(2, p.getVariables().size());
   assertEquals("FOO", ((Variable) p.getVariables().get(0)).getEnvName());
   assertEquals("//foo", ((Variable) p.getVariables().get(0)).getEnvExpr());
   assertEquals("BAR", ((Variable) p.getVariables().get(1)).getEnvName());
   assertEquals("//bar", ((Variable) p.getVariables().get(1)).getEnvExpr());
 }
 @Test
 public void constructorAllNull() throws XPathExpressionException {
   SubscriptionProperties p = new SubscriptionProperties(null, null, null);
   assertEquals(null, p.getNode());
   assertEquals("", p.getFilter());
   Object filter = p.getFilterXPath();
   assertEquals("XPathExpressionHandler", filter.getClass().getSimpleName());
   Object vars = p.getVariables();
   assertEquals("ArrayList", vars.getClass().getSimpleName());
 }