How to Test CLI Tools: A Practical Guide for Node.js Developers

How to Test CLI Tools: A Practical Guide for Node.js Developers You built a CLI tool. It works when you run it manually. But how do you write automated tests for something that reads from stdin, writes to stdout, exits with specific codes, and interacts with the file system? Testing CLI tools is different from testing libraries or APIs. There's no function to import and assert against — your "interface" is a process that takes arguments and produces output. This guide shows you how to test that process reliably. The Testing Challenge CLI tools have unique testing requirements: Process exit codes need to be verified stdout and stderr need to be captured separately File system side effects need isolation Interactive prompts need simulation Arguments and flags need combinatorial testing Piped input needs to work correctly Let's tackle each one. Setup: Use Vitest (or Jest) with execa npm install -D vitest execa execa is the key ingredient. It runs child processes and gives you clean access