tdd-masterlisted

# TDD Master Skill Test-Driven Development methodology for writing reliable, maintainable code. ## When to Activate This skill activates automatically when: - Implementing new features (write tests FIRST) - Fixing bugs (reproduce with failing test FIRST) - Writing or reviewing tests - Refactoring code (ensure tests exist) ## Core Workflow: Red-Green-Refactor ### Step 1: Test List Before coding, create a list of scenarios: ```markdown ## Test List for [Feature] - [ ] Happy path: main scenario - [ ] Edge case: empty input - [ ] Edge case: boundary values - [ ] Error case: invalid input - [ ] Error case: external service failure ``` ### Step 2: RED - Write Failing Test Write test that defines expected behavior: ```python def test__{what}__{scenario}__{outcome}(): # Arrange order = Order(items=[Item(price=1500)]) # Act discount = calculate_discount(order) # Assert assert discount == Decimal('150') ``` **CRITICAL**: Predict HOW the test will fail before running. ### Step 3: GREEN - Minimal Code Write **MINIMUM** code to pass: - Hardcoded values OK - Simple if-statements OK - "Fake it till you make it" OK ### Step 4: REFACTOR After test passes: - Remove duplication - Improve naming - Extract helpers - Keep tests green ### Step 5: REPEAT Next test from list until complete. ## Three Laws of TDD (Uncle Bob) | # | Law | |---|-----| | 1 | Cannot write production code without failing test | | 2 | Cannot write more test than sufficient to fail