Test-Driven Development (TDD) with Claude Code

This lesson introduces test-driven development (TDD) as a powerful workflow for building with Claude Code. It starts by framing when testing matters — quick internal tools might not need it, but anything with real users or higher stakes benefits from having the agent self-test its work. Without tests, the agent just writes code and re-reads it, declaring "looks good to me" without any objective verification. TDD changes that by giving the agent a real pass/fail signal, building on the spec-driven development approach covered earlier in the course.

The lesson walks through the Red-Green-Refactor cycle and demonstrates it live by building a to-do list app from scratch using plan mode and a TDD approach. Claude writes failing tests first, then builds the features to make them pass, resulting in a full test suite that verifies everything works. You'll see that prompting Claude for TDD is as simple as including "take a TDD approach" in your instructions.

Topics covered:

• When testing matters (and when it doesn't) based on project stakes
• Why TDD matters more with AI agents — alignment, not just quality
• The Red-Green-Refactor cycle explained
• How to prompt Claude Code to take a TDD approach
• Live demo: building a to-do list app with TDD in a Rails project
• Running and verifying the test suite yourself
• How test coverage prevents regression as codebases grow