Write a failing test. You’re writing your tests before your app code, so you know this test is going to fail. You haven’t implemented the feature yet! This is considered the “red” state (some tests failing).

Make the test pass. Here you write your app code, so you actually implement whatever functionality the test is looking at. Once you have your test passing, you’re now in the “green” state (all tests passing).

Refactor. Now that your test is passing, go make your code better. As the famous quote from Kent Beck goes: “Make it work. Make it right. Make it better. In that order.” Note that we don’t refactor until we’re in the “green” state. By having all our tests passing, we can refactor with confidence because if we break something, tests will start failing again, letting us know our refactor isn’t working perfectly yet.

Repeat. Go write another test now! Continue to loop through steps 1–3 as you write more tests and implement more functionality in your app.