请问什么是“defect injection”缺陷注入？

This technique is also call fault seeding and testing
(Mills, 1972). The idea is to inject known faults into the software system, and then use
testing to catch both injectedseeded faults and original faults to ensure that certain
types of defects are detected and removed, much like what immunization do to keep
people healthy.

将Defect注射到源程序中。因为很多Defect很不容易在某种机器环境中出现，比如一个用户的机器内存特别少的时候，微软要求程序仍然不能丢失数据和发生安全漏洞，但测试人员不能把测试机器的内存拆下来，也不能非常精确的把内存消耗到期望的数值，这时他们会通过注射一段代码来模拟内存的分配。

much like what immunization do to keep
people healthy.
really good example