"Imagine you are a QA engineer working on a critical software project. The project follows a standard Software Development Life Cycle $($SDLC$)$ comprising phases such as requirements gathering, design, implementation, testing, deployment, and maintenance. Your task is to plan and execute a comprehensive testing strategy that incorporates both white box and black box testing methodologies.

$1.$ Define the key objectives and goals of software testing within the context of the SDLC$.$