Month: December 2017


Why Unit Test?

Contrary to popular belief, the purpose of unit tests is not to verify correctness of code. Correctness can only be determined by a human. Code can be beautifully engineered and thoroughly unit tested, yet incorrect. The purpose of unit testing is more nuanced: to prevent changes to the expected behavior. When we write unit tests, we are formally specifying the expected behaviors of the testSubject. Whether of not these expectations are the correct expectations is purely subjective. When all of the expected behavior of our code is being witnessed by unit tests, we have a ‘safety net’ in place that allows us to […]


Test Driven Development (TDD) Tutorial

Introduction: Kent Beck, one of the original signers of the Agile manifesto and creator of eXtreme Programming, is credited with discovering Test Driven Development (TDD), but he claims he merely re-popularized the technique and coined the term. Here is what he had to say about rediscovering the technique: “The original description of TDD was in an ancient book about programming. It said you take the input tape, manually type in the output tape you expect, then program until the actual output tape matches the expected output. After I’d written the first xUnit framework in Smalltalk I remembered reading this and […]