Testing in Layers [EuroPython 2017 - Talk - 2017-07-10 - PythonAnywhere Room] [Rimini, Italy] The role of automated testing at the heart of modern development and operations is a given. However, the traditional approach to testing, separating too-developer-focused unit testing and (often only semi-automated) end-to-end integration testing—is not optimal in the modern, fluid world of DevOps. Nothing short of full automation is suitable for continuous integration; any “testing” requiring humans has a drastically different place in the continuum of development and deployment and should best be called by a completely different name like quality assurance. Within the realm of fully automated testing, the best approach, just as for other kinds of software, is modular and layered. This talk highlights the proper design of components for testing purposes and explains how such a design lets you compose multiple, layered testing suites that span the gamut from fast, light-weight unit tests meant to run all the time during development, to full-fledged end-to-end tests of whole systems—and, crucially, the often-neglected intermediate layers, bridging the thoroughness of end-to-end tests with unit tests’ speed and ability to pinpoint the location of any problems that emerge, enabling rapid fixes of most such problems. The talk also discusses the use of modular, layered testing components to validate software refactoring, and (when deployed in a load-testing arrangement) identify and validate software (and architectural) optimizations