如何在Junit测试中测试构造函数？

Question

如何在Junit4测试用例中测试此Fraction构造函数？ 谢谢！

public class Fraction {

    private int num;
    private int den;

    public Fraction(int num,int den){
        this.num=num;
        this.den=den;
        if(den==0){
            this.den=1;
            System.out.println("ERROR: DENOMINATOR CAN NOT BE 0");
            System.out.println("Now the fraction is changed to"+toString());
        }
    }
}

Answer 1

我运行构造函数，然后检查分母是否包含您期望的值：

public class FractionTest() {
    private Fraction f;

    @Test
    public void testLegalConstruction() {
        f = new Fraction (4, 7);
        assertEquals ("wrong num", 4, f.getNum());
        assertEquals ("wrong den", 7, f.getDen());

    @Test
    public void testIlegalConstruction() {
        f = new Fraction (3, 0);
        assertEquals ("wrong num", 3, f.getNum());
        assertEquals ("wrong den", 1, f.getDen()); // Note the 1
}