1. Write all the failing tests (RED phase) You need to write all the tests needed for your current task up-front, only then can you proceed. This must include edge cases and pathological as well as the happy-path cases.
2. Verify the tests fail due to the behavior of the application, and NOT due to the test. If you have more than one test that you need to write, you should write all of them before moving to the GREEN phase.
3. Write the minimal amount of code necessary to make the test pass (GREEN phase)
4. Verify the test now passes due to the behavior of the application.
5. Refactor the code to clean it up.
6. Verify tests still pass.

Red-Green-Refactor In Depth