Choosing the right testing methodology, such as smoke or sanity testing, is crucial for maintaining software quality and stability. Smoke testing, also known as build verification testing, offers a broad evaluation of an application's core functionalities to ensure build stability before further testing. It helps identify major issues early in the development process. Sanity testing, on the other hand, provides targeted validation of specific changes or fixes, ensuring recent modifications haven't adversely affected core functionalities. Both smoke and sanity testing play significant roles in the software development lifecycle, aiding in the early detection and rectification of defects, thus minimizing the risk of costly errors. Integrating feature flags with these testing methodologies enhances testing efficiency by allowing developers to enable or disable specific functionalities, facilitating safer deployments and controlled rollouts of new features. Automation tools like Selenium, Jenkins, and Cypress are often used to streamline the execution of smoke and sanity tests, providing rapid feedback on build stability and functionality. Employing these strategies fosters collaboration among cross-functional teams and promotes continuous improvement in software development practices.