tdd-stub-firstlisted

# TDD & Stub-First Strategy ## 1. Stubbing Phase 1. **Create Structure:** Files, classes, methods. 2. **Implement Stubs:** Use `NotImplementedError`, `return None`, or hardcoded values. 3. **Docstrings:** Add detailed docstrings describing future logic. 4. **E2E Test (Stub):** Write an E2E test that asserts the hardcoded behavior. - *Example:* asserting `discount == 100.0` (stubbed value). ## 2. Implementation Phase 1. **Verify Stubs:** Ensure E2E test passes on stubs. 2. **Replace Stubs:** Implement real logic. 3. **Unit Tests:** Add unit tests for specific methods and edge cases. 4. **Update E2E:** Update E2E test to assert real behavior. - *Example:* asserting `discount == 150.0` (calculated value). ## 3. Testing Rules - **No Mocking LLMs:** Use recorded responses or separate integration environments. - **Regression:** Always run full regression suite.