The Three Rules of TDD

Over the years I have come to describe Test Driven Development in terms of three simple rules. They are:

1. You are not allowed to write any production code unless it is to make a failing unit test pass.
2. You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures.
3. You are not allowed to write any more production code than is sufficient to pass the one failing unit test.

这些年来，我喜欢下面三条简单的规则来描述测试驱动开发：

1. 除非这能让失败的单元测试通过，否则不允许去编写任何的产品代码。
2. 只允许编写刚好能够导致失败的单元测试。 （编译失败也属于一种失败）
3. 只允许编写刚好能够导致一个单元测试失败的产品代码。