test-driven-development

test driven development involves writing the test before you write the code. the famous cycle is:

1. red - write a failing test (fails because feature doesn’t exist yet)
2. green - write the smalled amount of code required to make the failing test case pass
3. refactor - clean up the code while keeping the test green

repeat this in small incremental cycles implementing features.

TDD enables:

• test-first mindset forcing clear understanding of requirements before implementation
• smaller increments reduce risk + cognitive load
• continuous feedback

focus on behavior, not implementation details (avoid over-mocking internals).

practices:

• start with the simplest failing case, then add edge cases
• keep tests fast and independent
• refactor aggressively
• use it for new code or when changing existing code (characterization tests first).

---

related:

• v-model
• architecture-decision-records
• c4-model