conftest.py: shared fixtures
Overview
**conftest.py** is a special pytest file used to share fixtures across multiple test files. Any fixture placed in `conftest.py` is automatically available to all tests in that folder, without needing to import it. Here is a worked example showing two files in a folder: ```python # File: conftest.py import pytest @pytest.fixture def fake_user(): return {'name': 'Amit'} ``` ```python # File: test_profile.py # Notice there is no import statement for fake_user! def test_user_name(fake_user): assert fake_user['name'] == 'Amit' ``` pytest automatically discovers `conftest.py` and loads `fake_user`. `test_profile.py` can use it instantly. Now, look at this faded example where one step is blank: ```python # File: test_orders.py def test_cart(_______): assert fake_user['name'] == 'Amit' ``` To use the fixture from `conftest.py`, we fill in the blank with `fake_user`. We do not need an import statement.
When projects grow, you will have many test files needing the same setups (like test databases or fake users). `conftest.py` prevents you from copying the same fixtures everywhere.
Where used: pytest setups across multiple directories
Why learn this
- Scaling tests across multiple files efficiently.
- Centralizing expensive setup code like database connections.
Code walkthrough
# Simulated behavior of pytest
def conftest_fixture():
return 'SharedData'
def test_my_func(data):
print(f'Using {data}')
# pytest automatically does this:
test_my_func(conftest_fixture())Focus: test_my_func(conftest_fixture())
Aha moment
# File: conftest.py
import pytest
@pytest.fixture
def config(): return 'Global'
# File: test_local.py
import pytest
@pytest.fixture
def config(): return 'Local'
def test_mode(config):
print(config)Prediction: What does test_mode print? 'Global' or 'Local'?
Common guess: 'Global', because conftest.py affects everything.
It prints 'Local'. If a test file defines a fixture with the same name as one in `conftest.py`, the local file's fixture overrides the shared one for those tests.
Common mistakes
- Importing conftest: Writing `from conftest import fake_user` will cause errors or duplicate runs. Never import from `conftest.py`; pytest handles it automatically.
- Putting tests in conftest.py: Test functions (like `def test_something():`) should not go in `conftest.py`. It is only for shared fixtures and configuration.
Recall questions
- Explain conftest.py in your own words, as if to a classmate.
- Should you use an import statement to use a fixture from conftest.py?
Understanding checks
Where is the bug in this file?
The line `from conftest import db_fixture` is incorrect.
Fixtures in `conftest.py` are injected automatically by pytest. Explicitly importing from `conftest.py` breaks pytest's magic and leads to errors.
Can test_api.py in folderB use the secret_key fixture from folderA?
No, it cannot.
`conftest.py` only shares fixtures with tests in its own folder and subfolders. `folderB` is outside `folderA`'s scope.
Practice tasks
Use the shared fixture
Given a `conftest.py` that provides a `test_client` fixture, write the test function to use it without importing it.
Challenge
Create a shared fixture
Write the exact contents of a `conftest.py` file that creates a fixture named `api_url` which returns the string `'http://localhost'`.
Continue learning
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