TDD-Pytest Skill

Activate this skill when the user needs help with:

• Writing tests using TDD methodology (Red-Green-Refactor)
• Auditing existing pytest test files for quality
• Running tests with coverage
• Generating test reports to TESTING_REPORT.local.md
• Setting up pytest configuration in pyproject.toml

TDD Workflow

Red-Green-Refactor Cycle

1. RED - Write a failing test first

   • Test should fail for the right reason (not import errors)
   • Test should be minimal and focused
   • Show the failing test output

2. GREEN - Write minimal code to pass

   • Only implement what's needed to pass the test
   • No premature optimization
   • Show the passing test output

3. REFACTOR - Improve code while keeping tests green

   • Clean up duplication
   • Improve naming
   • Extract functions/classes if needed
   • Run tests after each change

Test Organization

File Structure

project/
  src/
    module.py
  tests/
    conftest.py          # Shared fixtures
    test_module.py       # Tests for module.py
  pyproject.toml         # Pytest configuration

Naming Conventions

• Test files: test_*.py or *_test.py
• Test functions: test_*
• Test classes: Test*
• Fixtures: Descriptive names (mock_database, sample_user)

Pytest Best Practices

Fixtures

import pytest

@pytest.fixture
def sample_config():
    return {"key": "value"}

@pytest.fixture
def mock_client(mocker):
    return mocker.MagicMock()

Parametrization

@pytest.mark.parametrize("input,expected", [
    ("hello", "HELLO"),
    ("world", "WORLD"),
    ("", ""),
])
def test_uppercase(input, expected):
    assert input.upper() == expected

Async Tests

import pytest

@pytest.mark.asyncio
async def test_async_function():
    result = await async_operation()
    assert result == expected

Exception Testing

def test_raises_value_error():
    with pytest.raises(ValueError, match="invalid input"):
        process_input(None)

Running Tests

With uv

uv run pytest                              # Run all tests
uv run pytest tests/test_module.py         # Run specific file
uv run pytest -k "test_name"               # Run by name pattern
uv run pytest -v --tb=short                # Verbose with short traceback
uv run pytest --cov=src --cov-report=term  # With coverage

Common Flags

• -v / --verbose - Detailed output
• -x / --exitfirst - Stop on first failure
• --tb=short - Short tracebacks
• --tb=no - No tracebacks
• -k EXPR - Run tests matching expression
• -m MARKER - Run tests with marker
• --cov=PATH - Coverage for path
• --cov-report=term-missing - Show missing lines

pyproject.toml Configuration

Minimal Setup

[tool.pytest.ini_options]
asyncio_mode = "auto"
testpaths = ["tests"]

Full Configuration

[tool.pytest.ini_options]
asyncio_mode = "auto"
asyncio_default_fixture_loop_scope = "function"
testpaths = ["tests"]
python_files = ["test_*.py", "*_test.py"]
python_functions = ["test_*"]
python_classes = ["Test*"]
addopts = "-v --tb=short"
markers = [
    "slow: marks tests as slow",
    "integration: marks integration tests",
]
filterwarnings = [
    "ignore::DeprecationWarning",
]

[tool.coverage.run]
source = ["src"]
branch = true
omit = ["tests/*", "*/__init__.py"]

[tool.coverage.report]
exclude_lines = [
    "pragma: no cover",
    "if TYPE_CHECKING:",
    "raise NotImplementedError",
]
fail_under = 80
show_missing = true

Report Generation

The TESTING_REPORT.local.md file should contain:

1. Test execution summary (passed/failed/skipped)
2. Coverage metrics by module
3. Audit findings by severity
4. Recommendations with file:line references
5. Evidence (command outputs)

Integration with Conversation

When the user asks to write tests:

1. Check conversation history for context about what to test
2. Identify the code/feature being discussed
3. If unclear, ask clarifying questions:
   • "What specific behavior should I test?"
   • "Should I include edge cases for X?"
   • "Do you want unit tests, integration tests, or both?"
4. Follow TDD: Write failing test first, then implement

Commands Available

• /tdd-pytest:init - Initialize pytest configuration
• /tdd-pytest:test [path] - Write tests using TDD (context-aware)
• /tdd-pytest:test-all - Run all tests
• /tdd-pytest:report - Generate/update TESTING_REPORT.local.md