@Test
public void twoSum() {

    Expression expr = new Expression();
    expr.numbers.add(new BigDecimal("12.1"));
    expr.operators.add(Expression.Operator.ADD);
    expr.numbers.add(new BigDecimal("-24.8"));
    BigDecimal result = expr.evaluate(false, 8, RoundingMode.HALF_UP);
    assertEquals(result, new BigDecimal("-12.7"));
}