TL;DR Test coverage and code quality metrics are essential tools for evaluating the health and maintainability of codebases, helping full-stack developers write clean, efficient, and reliable code that meets project requirements. Test coverage measures the percentage of code executed during automated tests, while code quality metrics provide insights into maintainability, readability, and performance. By incorporating these metrics into development workflows, developers can catch bugs early, improve code quality, reduce technical debt, and ensure their code is reliable, efficient, and easy to maintain.