软件测试作业题2道

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

 

Answer:

1. fault:  i>0  should  be  i>=0
2. a test case that does not execute the fault:

x=[ ];  y =2  Expected: NullPointerException    Actual: NullPointerException

3. a test case that executes the fault, but does not result in an error state:

x=[2,3,5];  y=3     Expected:1    Actual: 1

4. a test case that results in an error, but not a failure:

x=[2,3,5];  y=4     Expected:-1    Actual: -1

 

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

2. a test case that does not execute the fault:

x=[ ];    Expected: NullPointerException    Actual: NullPointerException

3. a test case that executes the fault, but does not result in an error state:

x=[0];       Expected:0     Actual: 0

4. a test case that results in an error, but not a failure:

x=[2,3,5];    Expected:-1    Actual: -1