tdd

以红→绿→重构循环的规范化流程驱动测试优先开发并产出可保留的测试。

用红→绿→重构的循环把开发流程变成先写测试再写实现，保证每个周期都产出值得保留的测试。适合想采用测试优先、需要集成测试或在敏捷小步迭代中交付功能的场景。手册里列了好测试的标准、反模式和循环规则，按着做能明显提高测试质量和可维护性。

# Test-Driven Development

TDD is the red → green loop. This skill is the reference that makes that loop produce tests worth keeping: what a good test is, where tests go, the anti-patterns, and the rules of the loop. Every section applies on every cycle — consult them before and during the loop, not after.

When exploring the codebase, read `CONTEXT.md` (if it exists) so test names and interface vocabulary match the project's domain language, and respect ADRs in the area you're touching.

## What a good test is

Tests verify behavior through public interfaces, not implementation details. Code can change entirely; tests shouldn't. A good test reads like a specification — "user can checkout wi