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.
a)
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 b)
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
1.Identify the fault.
a)i>0 should be i>=0
b)for (int i = 0; i < x.length; i++)should be for(int i = x.length - 1; i >= 0; i --)
2.If possible, identify a test case that does not execute the fault. (Reachability).
a) x=[2] y = 2;
b) all input will execute the fault.
3.If possible, identify a test case that executes the fault, but does not result in an error state.
a)x = [2,3,4] y = 3
b)x=[0]
4.If possible identify a test case that results in an error, but not a failure.
a) x=[2,3,4] y=5
b) x = [3,0,8]