@Test
public void equality() throws Exception {

  Expression expression = parseExpression("5 eq 5");
  assertEquals("{5 EQ 5}", expression.toString());
  expression = parseExpression("5 ne 5");
  assertEquals("{5 NE 5}", expression.toString());
  assertEquals("{1 EQ null}", parseExpression("1 eq null").toString());
  assertEquals("{null NE 2}", parseExpression("null ne 2").toString());
  assertEquals("{null EQ null}", parseExpression("null eq null").toString());
  wrongExpression("5 eq '5'");
  
}