Software testing foundations homework2

Homework 2

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.

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

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

56

Questions

 Identify the fault.
 If possible, identify a test case that does not execute the

fault. (Reachability)

 If possible, identify a test case that executes the fault, but does not result in an error state.

 If possible identify a test case that results in an error, but not a failure.

 Due Date: 23:59:59 March 15.

 Please send your answer to [e-mail] and post it to your blog.

解:

 

1.

1)for循环里的条件应为i>=0,否则到0直接return-1了.

2)test: x=[]; y = 2

3)test: x=[2, 3, 5]; y = 5

4)test: x=[2, 3, 5]; y = 9

2.

1)for循环应该从数组最后一位开,否则找到的是第一个0

2)test: x=[]

3)test: x=[1, 1, 1]

4)test: x=[0, 1, 1]