软件测试-作业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. 

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.

 

Answer：

Program1:

 1 public int findLast (int[] x, int y) { 
 2 //Effects: If x==null throw NullPointerException
 3 // else return the index of the last element 
 4 // in x that equals y.
 5 // If no such element exists, return -1
 6 for (int i=x.length-1; i > 0; i--)
 7 {
 8 if (x[i] == y) {
 9 return i; }
10 }
11 return -1;
12 }
13 // test: x=[2, 3, 5]; y = 2 
14 // Expected = 0

(1) i>0 should be i>=0

   (2) x=[ ]; Expected: NullPointerException; Actual: NullPointerException

   (3) x=[1,2,3]; y=2; Expected: 1 Actual: 1

   (4) x=[1,2,3]; y=4; Expected: -1; Actual: -1

 

Program2:

 1 public static int lastZero (int[] x) { 
 2 //Effects: if x==null throw NullPointerException
 3 // else return the index of the LAST 0 in x. 
 4 // Return -1 if 0 does not occur in x
 5 for (int i = 0; i < x.length; i++)
 6 {
 7 if (x[i] == 0) {
 8 return i; }
 9 } return -1; }
10 // test: x=[0, 1, 0]
11 // Expected = 2

(1)for(int i = 0; i < x.length; i++) should be for(int i = x.length-1; i>=0; i--)

   (2)x=[ ]; Expected: NullPointerException; Actual: NullPointerException

   (3)x=[1,2,3]; Expected: -1; Actual: -1

   (4)x=[0]; Expected: 0; Actual: 0