In the green step, you write the simplest code that makes the test pass. It doesn't matter whether the code you write is good and clean. The code can also be silly and even wrong. It is enough when all the tests pass. The name green refers to how most IDEs indicate a passing test. Xcode uses a green diamond with a white check mark.

It is very important that you try to write the simplest code that makes the tests pass. By doing so, you only write code that you actually need and that is the simplest implementation possible. When I say simple, I mean that it should be easy to read, understand, and change. The code should always be easy to understand.

Often the simplest implementation will not be enough for the feature you try to implement, but still enough to make all the tests pass. This just means that you need another failing test to further drive the development of that feature.