Feature Implementation Pattern

This skill defines the standard workflow for implementing features from your project's requirements or implementation plan.

Implementation Workflow

1. Read Requirements

• Locate the feature/requirement in your project documentation
• Understand the requirements, acceptance criteria, and test coverage expectations
• Identify files to create/modify
• Note any specification references

2. Create TODO List

Use

todo_write

tool to track implementation tasks:

todo_write(merge=False, todos=[
    {'id': 'feature_implementation', 'content': 'Implement feature X', 'status': 'in_progress'},
    {'id': 'feature_tests', 'content': 'Write tests for feature X', 'status': 'pending'},
    {'id': 'feature_docs', 'content': 'Update documentation', 'status': 'pending'}
])

3. Implement Code

• Create/modify source files as specified
• Follow project conventions (type hints, docstrings, error codes)
• Use established patterns and models
• Implement error handling with custom error codes
• Add necessary imports

4. Write Tests

Follow the test-writing pattern:

• Write incremental tests first (for development)
• Then verify acceptance criteria
• Use descriptive test names
• Add type annotations:

  -> None

• Test both success and error cases

5. Run Quality Checks

Before marking complete:

• Run linters:

  ruff

  and

  black

• Run type checker:

  mypy --strict --explicit-package-bases src/

• Run tests:

  pytest tests/ -v

• Ensure all tests pass before proceeding
• Fix any issues

6. Update Documentation

Update project documentation:

• Mark feature as complete in relevant docs
• Add Implementation Notes section with key details
• Update test coverage documentation
• Update acceptance criteria status
• Update any API or user documentation

7. Commit and Push

Only commit after all tests pass and quality checks succeed.

Follow commit format conventions:

feat(<scope>): Implement <feature name>

- [List of key implementations]
- [Key features added]

Tests:
- [List of tests added]

Files:
- [List of files changed with descriptions]

Important: Only commit after:

• ✅ All tests pass (

  pytest tests/ -v

  )
• ✅ Linters pass (

  ruff

  and

  black

  )
• ✅ Type checker passes (

  mypy

  )
• ✅ Documentation updated
• ✅ Feature verified to work correctly

After committing, push to GitHub automatically.

Feature Types

Core Business Logic

• Implement domain models and business rules
• Add validators for data integrity
• Write comprehensive unit tests
• Target: 100% coverage on core logic

Service Layer

• Implement service logic
• Write comprehensive unit tests
• Test all edge cases and error scenarios
• Target: ≥90% coverage on services

API Endpoints

• Follow API endpoint implementation patterns
• Create REST routes
• Write integration tests with test client
• Verify acceptance criteria

UI Components

• Implement user interface components
• Write component tests
• Test user interactions and state management
• Verify accessibility and responsiveness

Common Patterns

Error Handling

• Use consistent error codes
• Return appropriate result wrappers with error codes
• Return HTTP status codes for API endpoints
• Follow error handling patterns

Test Organization

• Unit tests:

  tests/unit/<module>/test_<component>.py

• Integration tests:

  tests/integration/test_<feature>.py

• API tests:

  tests/integration/api/test_<endpoint>.py

File Structure

• Source files: Follow project structure conventions
• Test files mirror source structure
• Follow naming conventions (snake_case for Python)

Best Practices

1. Read implementation plan: Always read

   docs/implementation-plan.md

   first to understand requirements, acceptance criteria, and test specifications
2. Track internally: Use TODO list for internal progress tracking (this is your internal mechanism, not part of the spec)
3. Test-driven: Write tests as specified in the implementation plan - tests are called out in the plan with specific acceptance criteria
4. One at a time: Only implement one section/sub-phase at a time. Wait for explicit user command before proceeding to the next section/sub-phase.
5. Verify AC: Ensure all acceptance criteria from the plan are met
6. Update plan: Mark features complete in

   docs/implementation-plan.md

   immediately after implementation
7. Commit frequently: Commit after each completed sub-phase, then push to GitHub

Edge Cases

When Implementation Differs from Plan

• Update the plan to reflect actual implementation
• Document deviations in Implementation Notes
• Ensure acceptance criteria are still met

When Tests Reveal Issues

• Fix issues in code before marking complete
• Update plan if requirements change
• Document lessons learned

When Multiple Files Need Updates

• Group related changes in single commit
• Use detailed commit message with file list
• Ensure all tests pass before committing