Test-Driven Development (TDD) FAQs

Question 1

What is the 'Iron Law' of this TDD skill?

Accepted Answer

The Iron Law states that no production code should be written until a failing test exists. If production code is written before a test, it must be deleted and restarted from the test-first phase.

Question 2

Does this skill support multiple programming languages?

Accepted Answer

Yes, it includes specific references and implementation patterns for various environments, including TypeScript (Jest/Vitest) and Rust (cargo test).

Question 3

Can I skip TDD for very simple functions?

Accepted Answer

No. The skill is designed to prevent rationalization. Even 'simple' code can break, and the TDD cycle ensures that every piece of logic is systematically verified from the start.

Question 4

When should I use the TDD skill in Claude Code?

Accepted Answer

You should use it for all new features, bug fixes, and refactoring. The only exceptions are throwaway prototypes, purely generated code, or configuration files containing no logic.

Question 5

Why is it mandatory to watch a test fail first?

Accepted Answer

Watching a test fail (the Red phase) confirms that the test is valid and specifically testing the missing behavior, rather than passing accidentally due to existing code or configuration.

Test-Driven Development (TDD)

Key Features

Use Cases

Test-Driven Development (TDD)

Key Features

Use Cases