1. Identify the fault.
for循环的结束条件错误，少第一个元素，即:x[0]。
应该是：i >= 0。
2. If possible, identify a test case that does not execute the fault. (Reachability)
x = [], y = 2;
3. If possible, identify a test case that executes the fault, but does not result in an error state.
x = [2,2,2], y = 2;
4. If possible identify a test case that results in an error, but not a failure.
x = [2,3,5], y = 0;
1. Identify the fault.
查找数组的最后一个0， 应该从后向前遍历数组。 即： for ( int i = x.length; i >= 0; i-- )
2. If possible, identify a test case that does not execute the fault. (Reachability)
x = [];
3. If possible, identify a test case that executes the fault, but does not result in an error state.
x = [1,2,3];
4. If possible identify a test case that results in an error, but not a failure.
x = [1 , 0];