Take a look at tools like Istanbul for Node.js and Simplecov for Ruby on Rails. https://coveralls.io/ https://coveralls.io/ has a nice list of code coverage too

Take a look at tools like Istanbul for Node.js and Simplecov for Ruby on Rails. https://coveralls.io/ https://coveralls.io/ has a nice list of code coverage tools for many languages. If you don't have tests, it is an extremely manual process to change anything about your codebase (including dependencies) and have any confidence that you haven't broken things. Once you write tests, code coverage lets you figure out what code is not being tested.