> For the complete documentation index, see [llms.txt](https://heronyang.gitbook.io/clean-up-your-spaghetti/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://heronyang.gitbook.io/clean-up-your-spaghetti/3_ideal_coding_process_and_principles/test_driven_development.md).
# Test Driven Developement
## Cycle
* Add a test
* Run all tests and see if the new one fails
* Write some code
* Run tests
* Refactor code
Repeat
## Why
* Immediate feedback (bugs are found earlier)
* Make sure you don't break previous code
* Help refactor code (don't have to worry too much) ex. better policy
## Why Not
(from [Stackoverflow](http://stackoverflow.com/questions/64333/disadvantages-of-test-driven-development))
* Big time investment
* Additional Complexity
* Design isn't clear at first
## Practice
Create a folder and add following files:
* index.html
```markup
TDD Practice
```
* tests.js
```javascript
QUnit.test("hello test", function( assert ) {
assert.ok( 1 == "1", "Passed!" );
});
QUnit.test('max', function (assert) {
});
QUnit.test('isOdd', function (assert) {
});
```
Then, let's start to edit `main.js`! Our goal is to **write unit tests first** and **implement main.js to pass all the tests**.
## Reference
* [Getting Started with QUnit](http://www.sitepoint.com/getting-started-qunit/)