测试驱动开发的主要步骤是什么

1. Write a single test
　　 2. Compile it. It shouldn’t compile because you’ve not written the implementation code
　　 3. Implement just enough code to get the test to compile
　　 4. Run the test and see it fail
　　 5. Implement just enough code to get the test to pass
　　 6. Run the test and see it pass
　　 7. Refactor for clarity and “once and only once”
　　 8. Repeat