Software Testing 软件测试 HW2 Fault Error Failure

There are two programs.

For program 1

public int findLast(int[] x, int y){
  //Effects: If x==null throw NullPointerException
  //else return the index of the last elements
  //in x that equals y.
  //If no such elements exists, return -1
  for(int i=x.length-1; i>0; i--)
  {
      if(x[i] == y)
      {
         return i;
      }
  }
  return -1;
}    

1、Identify Identify the fault. 

　　　　i > 0, it should be i ≥ 0, the searching should be stopped at 0, not 1.

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

　　　　x=null,  y=2

　　　　It will not execute the statement i>0 where the fault locates. 

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

　　　　x=[0, 1, 2],  y=1

　　　　It will execute the statement i>0 and have the same state if i>0 is fixed by i≥0, not result in an error state.

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

　　　   x=[0, 1, 2],  y=3

　　　　It will have an error state if the fault is fixed, but will have the same results, both -1.

For program 2

public static int lastZero(int [] x){
  //Effects: ifx==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;
}

1、Identify Identify the fault. 

　　　　for(i=0; i<length; i++) should be for(i=length-1; i≥0; i--), it should search from end to start to get the index of the LAST 0.

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

　　　　x=null

　　　　It will not execute the statement where the fault locates. 

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

　　　　x=[0]

　　　　It will execute the statement where the fault locates and have the same state, if the fault is fixed.

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

           x=[1, 2, 3]

　　　　It will have an error state if the fault is fixed, but will have the same results, both -1.