This is spot on. You need tests so that, during the next REPL session, you don't make changes that broke your old ones. I do also agree that people should try o

This is spot on. You need tests so that, during the next REPL session, you don't make changes that broke your old ones. I do also agree that people should try out TDD, especially if tests are fast to run. But a REPL is powerful tool that should not be avoided. There's a reason it's being bundled with the latest JDK releases and is an essential part of LISP and other modern languages.