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:
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 { 10 return i; 11 } 12 } 13 return -1; 14 } 15 // test: x=[2, 3, 5]; y = 2 16 // 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.