You're agreeing with me there. "each one exercising a little piece of functionality". In Beck's approach the tests are added at each step for a simple functiona

You're agreeing with me there. "each one exercising a little piece of functionality". In Beck's approach the tests are added at each step for a simple functionality addition, which then gets implemented in the project to pass the test. These days unit tests are more commonly used as "every method is a unit to be tested completely", often after the implementation is already there.