软件测试作业二

     （1）findLast

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

(a)  Identify the fault:

for (int i=x.length-1; i > 0; i--)  ,"i>0" should be "i>=0",otherwise, the 0 index can not be included

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

test: x=null;y=1;

expected=null;

fact = null;

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

 test：x=[3,2,5];y=2

expected=1;

fact = 1;

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

 test:x=[3,2,5] ; y=6

expected = -1;

fact = -1;

(2)lastZero

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

(a)  Identify the fault:

for (int i = 0; i < x.length; i++), order should be from high to low ,should be "for (int i=x.length-1; i > 0; i--) "

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

no possible

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

 test：x=[1]

expected=-1;

fact = -1;

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

 test:x=[1,0,1] 

expected = 1;

fact = 1;

tips:

Software Fault : A static defect in the software (软件中的设计错误，就是代码本身就写错了） 

Software Failure : External, incorrect behavior with respect to the requirements or other description of the expected behavior （失效，与预期不一样，表现出来的）

Software Error : An incorrect internal state that is the manifestation of some fault （在运行过程中的）

 

 fault -> error -> failure,软件中的缺陷在运行时会产生error,当error累计到一定程度时会导致失效，这些都是bug