One 、 Traditional methods and TDD Method

1、 Some people think that writing unit tests after software coding （ traditional method ）, The process is as follows ：

shortcoming ： Writing unit tests after writing functional code will lead to unit tests “ Particle size ” It's coarser . For the same function code , If the TDD programme , The result may be 10 individual “ Small ” Single test to cover , Each single test is relatively simple and easy to understand , Readability and maintainability are good , The single test changes little during reconstruction ; If you write a single test in the traditional way , It's often done with 1 individual “ Big ” Single test to cover , This single test logic is more complex , Because it has a lot to measure , Readability and maintainability are poor .

2、 Later, more and more people chose to write unit tests before software coding , This approach becomes test first or test driven development （Test-Driven Development,TDD）, The process is as follows ：

    explain ： First write a failed test , Then create the product code , And make sure that this test passes , The next step is to refactor the code or create another test that will fail . The specific process is to write a small amount of function code first , Then write unit tests , Repeat the two processes , Until the function code development is completed . The result is ： Basically, the function code has been developed , Unit testing is almost complete .

（1） Write a test that will fail , To prove the lack of code or function in the product .
    When writing tests , Assume that the product code is already working , In this way, the failure of the test indicates that there are defects in the product code . This test will initially fail to compile , Only after adding the required code , Only after compiling can it pass , Then the test can run , But it will fail , Because the required functions have not been realized yet .

（2） Write product code that meets the test expectations , Make the test pass .
（3） Refactoring code .
    If the test passes , You can write the next unit test or refactor , Make the code more readable or remove duplicate code, etc . Refactoring can be done after writing multiple tests , It can also be done after each test . Refactoring is an important practice , He makes sure the code is easier to read , Better maintenance , At the same time, it can still pass all the tests written before .

  Two 、 Succeed in TDD Three core skills

Succeed in TDD Three skills are required ：
1、 Write excellent tests , You can maintain 、 Can be read 、 reliable .
2、 Write tests before coding .
3、 Good test design .