pytest-async-sqlalchemy

Database testing fixtures using the SQLAlchemy asyncio API

You can install "pytest-async-sqlalchemy" via pip from PyPI

$ pip install pytest-async-sqlalchemy

Setup

Providing a Session Scoped Event Loop

The first thing to do is to declare an event_loop fixture with the scope set as "session". You can copy & paste the code below to your conftest.py:

@pytest.fixture(scope="session")
def event_loop():
    """
    Creates an instance of the default event loop for the test session.
    """
    if sys.platform.startswith("win") and sys.version_info[:2] >= (3, 8):
        # Avoid "RuntimeError: Event loop is closed" on Windows when tearing down tests
        # https://github.com/encode/httpx/issues/914
        asyncio.set_event_loop_policy(asyncio.WindowsSelectorEventLoopPolicy())

    loop = asyncio.new_event_loop()
    yield loop
    loop.close()

This is required since pytest-async-sqlalchemy shares the database connection between tests for performance reasons, but the default event_loop fixture defined by pytest-asyncio is function scoped¹ (i.e., it kills the database connection after each test).

Providing Database URL and Initialization

pytest-async-sqlalchemy provides placeholders to configure and initialize the testing database: database_url and init_database. These two must be defined in your project conftest.py like below:

@pytest.fixture(scope="session")
def _database_url():
    return "postgresql+asyncpg://postgres:masterkey@localhost/dbtest"


@pytest.fixture(scope="session")
def init_database():
    from myprorject.db import metadata

    return metadata.create_all

The _database_url must be a session-scoped fixture that returns the database URL in SQLAlchemy standard. init_database must also be a session-scoped fixture that returns the callable used to initialize the database (in most cases, this would return the metadata.create_all function).

Usage

This plugin provides the following fixtures:

• db_session: An AsyncSession object bounded to the test session database. Database transactions are discarded after each test function, so the same database is used for the entire test suite (avoiding the overhead of initializing a database on every test).
• database: An URL to the initialized test session database.
• scoped_database: scoped_database provides a new database within the scope of the test function. The value of the fixture is a string URL pointing to the database.

Contributing

Contributions are very welcome. Tests can be run with tox, please ensure the coverage at least stays the same before you submit a pull request.

License

Distributed under the terms of the MIT license, "pytest-async-sqlalchemy" is free and open source software

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1. pytest-async-sqlalchemy can't provide its own event_loop since pytest plugins are not able to override fixtures from one another. So the only solution we have now is to aks the user to declare its own event_loop fixture. Suggestions on how to overcome that in a better way are welcome, hit us on the Issues section.