The Unicorn Project: A Novel about Developers, Digital Disruption, and Thriving in the Age of Data

by Gene Kim

When he nods, just as Maxine did with the middle-school girls, she proposes rewriting the code path using functional programming principles. Tom’s test case has a lot of mocks and stubs to simulate the production environment: a configuration server, a database, a message bus, a customer object factory . . . . She jettisons all of them, because those are not areas of the system she wants to test. Instead, she pushes all that input/output and side-effects to the edges and creates unit tests around how an incoming repair order message is processed, how customer data is transformed, and what outgoing messages are sent. She has each thread make its own copy of the customer object. They rewrite each object method into a series of pure functions—a function whose output is completely dependent upon its inputs, with no side-effects, mutations, or accesses to global state.