Explore the concept of layered testing in software development through this 45-minute EuroPython 2017 conference talk. Delve into the importance of automated testing in modern DevOps practices and learn why traditional approaches to unit and integration testing may fall short. Discover how to design modular and layered testing components that bridge the gap between thorough end-to-end tests and fast, pinpointed unit tests. Gain insights on using layered testing to validate software refactoring, identify optimizations, and support continuous integration. Examine topics such as semantic constraints, mocks vs. fakes, testing machine learning algorithms, and the relationship between tests and logging. Apply these principles to create more efficient and effective testing suites for your software projects.