A maintainable codebase should have clean and easy-to-manage code. In this course, Jon Peck shows how to gauge quality, implement testing, and measure code coverage in your Node.js apps. To help you better understand these key concepts, he walks through how to clean up a buggy restaurant booking app. First, Jon reviews testing and code quality fundamentals. Next, he shows how to find errors by linting your code base, and explores different testing frameworks and their components. Finally, he demonstrates how to write unit and functional tests to exercise the code base, then determine what code was executed with a code coverage report.