软件测试之随堂作业二
Below are two faulty programs. Each includes a test case that results in failure. Answer the following questions about each program.
案例一：
public int findLast (int[] x, int y) {
//Effects: If x==null throw NullPointerException
// else return the index of the last element
// in x that equals y.
// If no such element exists, return -1
for (int i=x.length-1; i > 0; i--)
{
if (x[i] == y) {
return i; }
}
return -1;
}
// test: x=[2, 3, 5]; y = 2
// Expected = 0
案例二：
public static int lastZero (int[] x) {
//Effects: if x==null throw NullPointerException
// else return the index of the LAST 0 in x.
// Return -1 if 0 does not occur in x
for (int i = 0; i < x.length; i++)
{
if (x[i] == 0) {
return i; }
}
return -1;
}
// test: x=[0, 1, 0]
// Expected = 2
Questions
1、 Identify the fault.
2、If possible, identify a test case that does not execute the fault. (Reachability)
3、If possible, identify a test case that executes the fault, but does not result in an error state.
4、If possible identify a test case that results in an error, but not a failure.
解答：
案例一：
1、由于数组的下标是从0开始的，所以for循环中的条件判断应该改为：（int i = x.length-1; i >= 0; i--)
2、test：x = [] (抛出空指针异常，没有执行下面的程序，则没有执行fault）
3、test：x = [3,2,5]; y = 2; Expected = 1
4、test: x = [3,2,5]; y = 1; Expected = -1
案例二：
1、题目要求找到最后一个0所在的数组下标，所以for循环中的条件判断应该改为：（int i = x.length-1; i >= 0; i--)
2、test：x = [] (抛出空指针异常，没有执行下面的程序，则没有执行fault）
3、test：x = [1,2,0]; Expected = 2
4、test: x = [3,2,5]; Expected = -1
(完，本文仅是有关作业的解释，并不用作他用）
