Gilly Barr discusses the importance of functional testing in addition to unit testing, sharing experiences with various testing tools and frameworks. Initially using Selenium with C# and Java, Barr encountered challenges and sought a JavaScript framework, eventually choosing Intern for its ability to handle both unit and functional tests under one runner, as well as its parallel testing capabilities and native AMD support. The blog emphasizes the importance of readability in tests and introduces the concept of "page objects" to abstract the details of web interactions, making tests easier to maintain and understand. Intern's built-in polling and promise-based methods enhance testing for single-page applications, and the framework's integration with tools like Jenkins allows for continuous deployment with the help of Docker containers. Barr highlights the significance of collecting data, including screenshots, when tests fail, to facilitate troubleshooting and improve test reliability.