@Test
public void testIsEmptyOperator() throws Exception {

  QueryLexer lexer = new QueryLexer();
  Token[] tokens = lexer.tokens("category1.isEmpty()");
  List<Token> listTokens = new ArrayList<Token>();
  listTokens.add(new Token(Token.TYPE.RELATIONAL_OPERATOR_FUNC, ".isEmpty("));
  listTokens.add(new Token(Token.TYPE.PROPERTY_OPERAND, "category1"));
  listTokens.add(new Token(Token.TYPE.BRACKET_CLOSE, ")"));
  assertArrayEquals(listTokens.toArray(new Token[listTokens.size()]), tokens);
}