How to Perform Test-Driven Development From the Command Line

A command-line test-driven development workflow centers on the red-green-refactor cycle, using test-runner exit codes and test counts to distinguish a real failed assertion from setup errors such as a missing module that prevents tests from running. The guide demonstrates JavaScript and Python workflows with Jest or pytest, watch modes for rapid feedback, and full-suite checks before commits, while emphasizing that coverage thresholds alone do not prove test quality and mutation testing can expose weak assertions. It extends the approach to acceptance testing with Playwright and Kane CLI, where tests are calibrated against a working reference, run red against an unfinished local feature, and replayed after implementation or refactoring, including browser-grid execution on TestMu AI. The material also describes giving a failing acceptance test to an AI coding agent as a fixed specification, using hooks to prevent the agent from stopping while unit tests fail, and requiring the agent to verify behavior in a real browser. Local Git hooks and CI pipelines then enforce the same unit, coverage, mutation, and acceptance-test exit-code gates on commits, pushes, and pull requests, while troubleshooting guidance covers common issues with zero-test runs, watchers, coverage branches, mutation tools, ports, and CLI test files.

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