The document discusses testing legacy Rails applications. It provides steps to get testing set up on a legacy Rails app, including creating a test database, running migrations, and getting Rake tasks to run tests. It emphasizes starting with one test at a time, finding and fixing bugs, and refactoring code. Examples are given of writing a model test based on application logs and fixing a failure by updating code. The document stresses treating methods as isolated boxes and only testing one thing at a time to incrementally add tests to a legacy codebase.