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DevOps is an iterative cycle of building, testing, and releasing software in short iterations. Testing is part of Continuous Delivery that assures quality at each stage of the delivery pipeline before moving on to the next stage. Automated tests check for functionality and make sure every line of code and feature works as intended. Manual and automated tests are suitable when opinion and nuance play a role, like user experience. Non-functional tests check the way a system operates rather than the functions of the system. The more tests you automate, the faster your application can iterate.