Smoke testing and regression testing are central methodologies in software testing, each serving distinct yet complementary roles in ensuring software quality and functionality. Smoke testing acts as a preliminary phase, quickly validating the basic functionality and stability of a new software build, providing immediate feedback on whether it is ready for further testing. In contrast, regression testing comprehensively examines the application to confirm that updates or changes do not introduce new defects, maintaining the overall integrity and reliability of the software over time. Both testing types benefit from automation, enhancing efficiency and accuracy, and can be further optimized through the use of feature flags, which allow selective testing of features and facilitate gradual and controlled feature rollouts. By leveraging these methodologies alongside feature flags, software testing professionals can effectively manage the complexities of software development, ensuring high-quality product delivery.