TDD Workflow
Write tests first, code second.
1. The TDD Cycle
🔴 RED → Write failing test
↓
🟢 GREEN → Write minimal code to pass
↓
🔵 REFACTOR → Improve code quality
↓
Repeat...
2. The Three Laws of TDD
- Write production code only to make a failing test pass
- Write only enough test to demonstrate failure
- Write only enough code to make the test pass
3. RED Phase Principles
What to Write
| Focus |
Example |
| Behavior |
"should add two numbers" |
| Edge cases |
"should handle empty input" |
| Error states |
"should throw for invalid data" |
RED Phase Rules
- Test must fail first
- Test name describes expected behavior
- One assertion per test (ideally)
4. GREEN Phase Principles
Minimum Code
| Principle |
Meaning |
| YAGNI |
You Aren't Gonna Need It |
| Simplest thing |
Write the minimum to pass |
| No optimization |
Just make it work |
GREEN Phase Rules
- Don't write unneeded code
- Don't optimize yet
- Pass the test, nothing more
5. REFACTOR Phase Principles
What to Improve
| Area |
Action |
| Duplication |
Extract common code |
| Naming |
Make intent clear |
| Structure |
Improve organization |
| Complexity |
Simplify logic |
REFACTOR Rules
- All tests must stay green
- Small incremental changes
- Commit after each refactor
6. AAA Pattern
Every test follows:
| Step |
Purpose |
| Arrange |
Set up test data |
| Act |
Execute code under test |
| Assert |
Verify expected outcome |
7. When to Use TDD
| Scenario |
TDD Value |
| New feature |
High |
| Bug fix |
High (write test first) |
| Complex logic |
High |
| Exploratory |
Low (spike, then TDD) |
| UI layout |
Low |
8. Test Prioritization
| Priority |
Test Type |
| 1 |
Happy path |
| 2 |
Error cases |
| 3 |
Edge cases |
| 4 |
Performance |
9. Anti-Patterns
| ❌ Don't |
✅ Do |
| Skip the RED phase |
Watch test fail first |
| Write tests after |
Write tests before |
| Over-engineer initial |
Keep it simple |
| Multiple asserts |
One behavior per test |
| Test implementation |
Test behavior |
10. AI-Augmented TDD
Multi-Agent Pattern
| Agent |
Role |
| Agent A |
Write failing tests (RED) |
| Agent B |
Implement to pass (GREEN) |
| Agent C |
Optimize (REFACTOR) |
Remember: The test is the specification. If you can't write a test, you don't understand the requirement.
When to Use
This skill is applicable to execute the workflow or actions described in the overview.
