    @Test
    public void givenSumExpressionWhenEvaluatingOperatorsThenResultIsCorrect() throws SetlException {

        // given
        FragmentList<AOperator> operators = new FragmentList<>();
        addNumber(operators, 10);
        addNumber(operators, 20);
        operators.add(Sum.S);

        // when
        EvaluationResult result = evaluate(operators);

        // then
        assertEquals("10 + 20", result.getExpression());
        assertEquals(INTERNAL_TERM_PREFIX + "sum(10, 20)", result.getExpressionTerm());
        assertEquals(30, result.getResultAsInt());
    }