@Test
 public void canNegateFloatValue() {
   NegateExpression negateExpression = new NegateExpression(new Constant(5.5f));
   queryEngine.visit(negateExpression);
   Assert.assertEquals(-5.5f, queryEngine.result);
   Assert.assertTrue(queryEngine.result instanceof Float);
 }
 @Test
 public void canNegateIntegerValue() {
   NegateExpression negateExpression = new NegateExpression(new Constant(5));
   queryEngine.visit(negateExpression);
   Assert.assertEquals(-5, queryEngine.result);
 }
 @Test
 public void canApplyNotOperator() {
   NotOperator notOperator = new NotOperator(new Constant(true));
   queryEngine.visit(notOperator);
   Assert.assertEquals(false, queryEngine.result);
 }