说明：  这是XMODEM传输协议原代码,测试只能证明错误的存在，而不能表明程序中没有错误。 测试的两个作用是：确定程序中缺陷的存在；有助于判断该程序在实际上是否可用。 软件测试最困难的问题之一是知道何时停止测试(When to stop testing? ) 自己测试自己的程序是不可能的。 当一个软件被测出的缺陷数目增加时，更多的未被发现的缺陷存在的概率也随之增加。
(This XMODEM transfer protocol source code, the test can only be proved wrong there and not show anything wrong procedure. The two test role is : procedures for determining the existence of defects; Contribute to the judge whether the procedure can be used in practice. Software testing the most difficult one of the problems is to know when to stop testing (When to stop testing) testing their own procedures is not possible. When a software detected the increase in the number of defects, more undiscovered flaws in the probability has increased.)