【软件测试作业】Error、Failure、Fault

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

Identify the fault.

for循环中i >0修改为i >= 0

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

x = null, y = 0

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

x = [2,3,4] , y = 4

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

x = [2,3,4] , y = 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

Identify the fault.

for循环中应该从后往前遍历修改为for(int i = x.length-1; i >= 0; i--)

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

x = null

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

x = [0]

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

x = [0,1,2]