Add test infrastructure post refactoring (issue #24)

[atarukun]

Summary

This PR implements the test infrastructure as specified in issue #24, adding comprehensive testing capabilities and linting configuration to the Slack MCP project.

Changes Made

1. Development Dependencies

• Added [project.optional-dependencies] section to pyproject.toml
• Included all required tools: pytest, pytest-asyncio, pytest-cov, flake8, mypy, black, isort

2. Tool Configuration

• Added comprehensive tool settings in pyproject.toml for:
  • black (line-length: 120)
  • isort (profile: black, line-length: 120)
  • mypy (Python 3.12, ignore missing imports)
  • pytest (test paths, async mode)
  • coverage (source paths, exclusions)
• Created .flake8 configuration file with max-line-length: 120 and appropriate ignores

3. Test Infrastructure

• Created tests/ directory with proper structure
• Added conftest.py with comprehensive fixtures:
  • Mock Slack clients (sync and async)
  • Sample API responses for channels, users, and messages
  • Mock MCP server instance
• Created unit test files for all 4 tool modules:
  • test_core.py - Tests for 7 core tools
  • test_message_management.py - Tests for 8 message tools
  • test_channel_management.py - Tests for 9 channel tools
  • test_user_management.py - Tests for 4 user tools
• Added test_utils.py for utility function tests
• Added test_integration.py for integration test framework

4. GitHub Actions CI/CD

• Created .github/workflows/test.yml with:
  • Python 3.12 test matrix
  • Pip caching for faster builds
  • Test execution with coverage reporting
  • Non-blocking linting checks (flake8, mypy, black, isort)
  • PR comment integration for linting results

5. Gitignore Updates

• Added missing Python patterns: *.pyc, .mypy_cache/
• Already had coverage and pytest cache patterns

Verification

• Tool count confirmed: 28 tools (7 + 8 + 9 + 4)
• All linters configured in check-only/notify-only mode
• Tests are discoverable by pytest
• GitHub Actions workflow has valid YAML syntax
• File operations references removed (as per codebase changes)

Testing

To run the tests locally:

pip install -e ".[dev]"
pytest tests/

To run linters (informational only):

flake8 src/
mypy src/
black --check src/
isort --check-only src/

Notes

• All linting is intentionally non-blocking to allow gradual code quality improvements
• Tests focus on mocking Slack API calls to avoid requiring real tokens
• Integration test framework is ready for future expansion

Closes #24