dev-tddlisted

# Test-Driven Development (TDD) ## Iron Law ``` NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST ``` If code was written before the test: delete it. Start over with TDD. - Don't keep it "as a reference" - Don't "adapt" it by writing the tests - Don't look at it - Delete = delete Implement from scratch starting from the tests. Period. ## TDD Cycle ``` ┌─────────┐ ┌─────────┐ ┌──────────┐ │ RED │ ──▶ │ GREEN │ ──▶ │ REFACTOR │ │ Test │ │ Code │ │ Clean │ │ fail │ │ pass │ │ up │ └─────────┘ └─────────┘ └──────────┘ ▲ │ └──────────────────────────────┘ ``` ## Phase 1: RED - Write a failing test ### Write ONE minimal test showing the expected behavior ```typescript describe('Module', () => { describe('function', () => { it('should [behavior] when [condition]', () => { // Arrange - Prepare // Act - Execute // Assert - Verify }); }); }); ``` ### Good test vs Bad test **Good**: Clear name, tests real behavior, one thing only ```typescript test('retries failed operations 3 times', async () => { let attempts = 0; const operation = () => { attempts++; if (attempts < 3) throw new Error('fail'); return 'success'; }; const result = await retryOperation(operation); expect(result).toBe('success'); expect(attempts).toBe(3); }); ``` **Bad**: Vague name, tests the mock instead of the code ```typescript test('retry works', async