Test-Driven Development

TDD is the red-to-green loop. Tests verify behavior through public interfaces, not implementation details, and each cycle lands one narrow vertical slice.

Process

1. Read the active project's CONTEXT.md, relevant ADRs, approved spec, and ticket before testing. Identify the highest existing public seam that demonstrates the required behavior. If a new seam is needed, propose it before writing tests.

   Done when the test seam is agreed and named in the implementation work.

2. Write one failing behavior test at that seam. Use an independent expected value and avoid internal mocks, private methods, call-order assertions, and database side-channel verification.

   Done when the test fails for the missing behavior.