The Test Automation Pyramid: A Model Misunderstood

Alan Richardson opens with a confession: he has never been a fan of the test automation pyramid. But after rereading the original source — Mike Cohn's 2008 book Succeeding with Agile — he realized his problem was not with Cohn's model, but with how everyone else had mangled it. The diagram that gets passed around at conferences and in blog posts is almost never Cohn's actual model. It is someone else's reinterpretation, still bearing Cohn's name, but carrying different assumptions, different definitions, and different implications.

The Original Model vs. The Proliferation of Variants

Cohn's original diagram had three layers: UI level, service level, and unit level. It appeared in chapter 16 of Succeeding with Agile, a throwaway diagram to make a simple point about automating at different levels. The variants that have since proliferated replace "service level" with API tests, integration tests, system tests, or component tests. Some add manual testing on top. Others swap in acceptance tests and unit tests. None of these are Cohn's model. They are new models that borrow the diagram but carry different assumptions.