TJU_SCS_软件测试_homework2

　　1.作业要求　　

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

　　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.

 

　　2.作业内容

　　2.1

　　program:

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

　　answer:

　　　　1. i > 0 so in array x, we can not get x[0], that means we miss an element.

　　　　2. test: x = []; y = 2.

　　　　3. test: x = [3, 2, 9]; y = 2. Expected: 1. Actual: 1. Do execute the fault but right answer.

　　　　4. test: x = [2, 1, 9]; y = 2. Expected: 0. Actual: -1. Wrong answer.

 

　　2.2

　　program:

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

　　answer:

　　　　1. variable i is 0 to x.length, but when x[i] equals to 0 at the first time return i not the last time. It may be okey if there is not more than 1 0 in x. 　　But it cause wrong answer when there is more than one 0 in x.

　　　　2. test: x = [1, 2, 3]; 

　　　　3. test: x = [1, 0, 2]; Expected: 1. Actual: 1. Do execute the fault but right answer.

　　　　4. test: x = [1, 0, 0]; Expected: 2. Actual: 1. Wrong answer.