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.
programs:
1.
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
answers:
1. The variable i should bigger than 0 or equals 0.
In this program i>0 is not right. It cannt get x[0].
2. test: x=[]; y=2
3. test: x=[3,1,5]; y=2
4. test: x=[2,3,5]; y=2
2.
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
answers:
1. The variable i should from x.length-1 to 0.
This program is scanning a wrong order which is from 0 to x.length-1. It's wrong.
This program means that once there is a 0 from the beginning of x, it will return
the position of i.
2. test: x=[];
3. test: x=[1,2,0]
4. test: x=[0,1,0]
after the question: This is an exercise to remind us of the RIP rules, which are Reachability, Infection and Propagation.
It's important to software testing.