HW2——Failure, Error, Fault

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 intfindLast(int[] x, inty) {

//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

 

1.Identify the fault.                    

i> 0 ,i>0会忽略数组中的第一个值，故应改为i>=0.     

2.If possible, identify a test case that does not execute  the fault. (Reachability)       

x=[]  y=4   expected=-1    actual=-1 

x=[1,2,3]  y=4   expected=-1     actual=-1 

x=[1,2,3]    y=2   expected=1     actual=1 

3.if possible, identify a test case that executes the fault, but not result in an error state 

x = [2, 3, 2, 6],  y=2  

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

x=[1]   y=4      expected=-1   actual=-1 

 

 

 

 

public static intlastZero(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

 

1.Identify the fault.     

应该从后遍历，for (int i=x.length-1; i >= 0; i--)

2.If possible, identify a test case that does not execute  the fault. (Reachability) 

程序总会执行int i=0 故肯定会执行Fault，即使x=null也会执行Fault。

3.if possible, identify a test case that executes the fault, but not result in an error state     

x=null  

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

x=[1, 0, 2]