Test-Driven Development

Iron Law

No production code without a failing test first.

No exceptions. Not for "simple" changes. Not for "obvious" fixes. Not under time pressure.

RED-GREEN-REFACTOR

1. RED — Write a failing test

• One minimal test with a clear name
• Use real code, not mocks (unless unavoidable)
• Watch it fail. Verify it fails for the RIGHT reason.

2. GREEN — Write minimal code to pass