我在spock框架中编写了一些单元测试。但是我的测试总是正确的，即使我通过了不正确的值。

class CalculatorTest extends Specification  {

def "Method should return roman number"() {
    given:
        CalculatorApi romanCalculator = Mock()
    when: "I add two numbers as integer"
        romanCalculator.add(2, 2)
    then: "Method should return roman number as String"
        romanCalculator.add(2, 2) >> 32131
}

方法“add”应返回字符串。在这个测试中，假设一个方法应该返回整数。

public class RomanCalculator implements CalculatorApi {

private RomanConverter romanConverter;

public RomanCalculator() {
    this.romanConverter = new RomanConverter();
}

public String add(int one, int two) throws OperationFail {
    int number = one + two;

    try {
        return romanConverter.convertNumber(number);
    } catch (NumberNotFound e) {
        throw new OperationFail(e.getMessage());
    }
}

public class RomanConverter implements ConverterApi {

public String convertNumber(Integer number) throws NumberNotFound {

    switch(number) {
        case 1: 
            return "I";
        case 2:
            return "II";
        case 3:
            return "III";
        case 4:
            return "IV";
        case 5:
            return "V";
        case 6:
            return "VI";
        case 7:
            return "VII";
        case 8:
            return "VIII";
        case 9:
            return "IX";
        case 10:
            return "X";
        default:
            throw new NumberNotFound();
    }
    }

为什么这个方法不起作用？我刚开始用mock学习单元测试。