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What Is TDD? Canon TDD, the Test List and the Real Purpose of Red-Green-Refactor

TDD is not writing lots of unit tests but a discipline of growing behavior in small steps while correcting the design all the time: a test list first, then one test from it, red, green, an optional refactor and an updated list. We look at Kent Beck's Canon TDD, how it differs from Uncle Bob's three laws, and how the list for Bookstore's CouponValidator changes over two loops, with real test output.