The software testing life cycle (STLC) is a crucial component in the software development process that ensures high-quality delivery by integrating a series of systematic stages, including requirement analysis, test planning, test case development, test environment setup, test execution, and test closure. By emphasizing testing early and often, the STLC aligns with the DevSecOps shift-left philosophy, helping to minimize risks, align testing efforts with business objectives, and reduce uncertainties. The stages of the STLC involve analyzing application requirements, planning and scheduling tests, developing test cases, setting up a testing environment that mirrors production conditions, executing tests with a focus on continuous integration, and finally, compiling and evaluating results to refine future testing strategies. Using a sample application, the guide illustrates how each stage can be applied, emphasizing the importance of prioritizing features, thorough documentation, and collaboration with stakeholders to ensure comprehensive test coverage and effective error detection.