In this episode we morph the simple acceptance test we wrote in the previous episode into an acceptance test that specifies what our application should do when quoting a stock price. We learn that sometimes initial acceptance tests are, in a sense, about exploration of the domain, and how to specify it, and that giving yourself permission to explore is important. We get to see what it means if an acceptance test can be satisfied with a hard coded implementation and why “Given/When/Then” is a sensible structure for such tests. We discover that test driving like this uncovers domain concepts and relationships, and we introduce “stubbing” to help us control our external environment.

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