public void testSignOperator() {
    String expr = "int x = 15; -x";
    Map vars = new HashMap();

    //  assertEquals(-15, MVEL.eval(expr, vars));
    vars.clear();

    Serializable s = MVEL.compileExpression(expr);
    assertEquals(-15, MVEL.executeExpression(s, vars));

    //  assertEquals(-15, test("int x = 15; -x"));
  }