pytest-testing

pytest Testing Patterns (stack-agnostic)

pytest is the standard test runner for modern Python projects. These patterns apply to any Python 3.10+ codebase regardless of framework.

Project layout

Keep tests outside the source tree so installed packages are tested rather than the raw source directory:

src/
  myapp/
    __init__.py
    service.py
    repository.py
tests/
  conftest.py
  test_service.py
  test_repository.py
  integration/
    conftest.py
    test_db.py
pyproject.toml

Configure pytest to find the source in pyproject.toml:

[tool.pytest.ini_options]
testpaths = ["tests"]
addopts = "--strict-markers -q"

Install the package in editable mode before running tests so import myapp resolves correctly:

pip install -e .        # or: poetry install / uv sync
pytest

conftest.py — shared fixtures

conftest.py files are loaded automatically by pytest. Place shared fixtures there instead of importing them into every test module.

# tests/conftest.py
from __future__ import annotations

import pytest

from myapp.database import Database, get_connection
from myapp.service import UserService


@pytest.fixture(scope="module")
def db() -> Database:
    """Module-scoped DB connection — created once per test module."""
    conn = get_connection(url="sqlite:///:memory:")
    conn.create_tables()
    yield conn
    conn.close()


@pytest.fixture
def user_service(db: Database) -> UserService:
    """Function-scoped service — fresh instance per test, shared DB."""
    return UserService(db)

Fixture scopes (from broadest to narrowest):

Scope	Created	Destroyed
session	Once per pytest run	After all tests
module	Once per test module	After last test in module
class	Once per test class	After last test in class
function (default)	Once per test function	After the test returns

Use the narrowest scope that avoids expensive re-creation. Use session scope only for truly global state (e.g., a Docker container started via pytest-docker).