Software Testing 2 —— Fault、error and failure小练习

Questions:

Below are two faulty programs. Each includes a test case that results in failure. Answer the following questions (in the next slide) about each program.

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.

Program One:

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

Answers:

1、错误代码：

for(int i = x.length-1; i > 0; i--)

原因：应共遍历x.length次，且数组下标从零开始。

改正为：

for(int i = x.length-1; i >= 0; i--)

2、A test case: x = [] ——> If x == null throw NullPointerException，不会执行fault。

3、A test case: x = [2, 3, 5]; y = 3 ——> The result is 1，执行了fault，且结果正确。

4、A test case: x = [2, 3, 5]; y = 4 ——> The result is -1，是error，不是failure。

---

Program Two:

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

Answers:

1、错误代码：

for (int i = 0; i < x.length; i++)

原因：返回的应该是最后一个零的位置，上述代码返回的是第一个零的位置，且数组下标从零开始。

改正为：

for (int i = x.length-1; i >= 0; i--)

2、A test case: x = [] ——> If x == null throw NullPointerException，不会执行fault。

3、A test case: x = [1, 0, 1] ——> The result is 1，执行了fault，且结果正确。

4、A test case: x = [2, 3, 5] ——> The result is -1，是error，不是failure。