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PyTest: Use fixtures

PyTest fixtures provide a fixed baseline so that tests execute reliably and produce consistent, repeatable results. Initialization may setup services, state, or other operating environments.

How To

Defined fixtures don’t have to be imported by the file containing the tests: they only have to be present in one of the higher-level conftest.py files. This makes them ideal for controlling the test suite.

Fixture for separating the preparation from the test

You can use a fixture to control the way tests run while keeping the tests themselves concise and focused.

Example:

conftest.py

import logging

@pytest.fixture(scope="session")
def setup_logger():
    logging.basicConfig()
    logger = logging.getLogger("test_logger").setLevel(logging.INFO)
    return logger

test_file.py

import pytest

def test_logger(setup_logger):
    test_logger = setup_logger
    test_logger.info("This message is sent by the test logger set up outside this test")
    ...

Fixture for setup and teardown

Fixtures can also be used to setup a test environment and then tear it down afterwards. This is especially important when working with servers or ETL jobs.

Example:

conftest.py

import logging
from custom_server import SomeServerController

@pytest.fixture()
def setup_then_teardown():
    # Set up the server
    server = SomeServerController()
    server.start()

    # Run a test function
    yield

    # Tear down the server
    server.stop()

This fixture could then be called by a test function to allow that test function to interact with this server.

References

• PyTest Docs: Fixtures