These patterns are about when you write tests, where you write tests, and when you stop writing tests.
Which test should you pick next from the list? Pick a test that will teach you something and that you are confident you can implement.
Each test should represent one step toward your overall goal. Looking at the following Test List, then, which test should we pick next?
Exchange one currency
Exchange two currencies
There is no right answer. What is one step for me, never having implemented these objects before, will be one-tenth of a step to you, with your vast experience. If you don't find any test on the list that represents one step, then ...