Pytest fixture for a class through self not as method argument

Question

Often I'll write a test class that uses a pytest fixture in every method. Here's an example. I'd like to be able to avoid having to write the fixture name in the signature of every method. It's not DRY. How can this be done?

I would like to be able to access the fixture by giving the fixture as an attribute of the test class. In this example, I would like to see the google fixture as an attribute of TestGoogle. Is this possible?

from bs4 import BeautifulSoup
import pytest
import requests

@pytest.fixture()
def google():
    return requests.get("https://www.google.com")


class TestGoogle:
    def test_alive(self, google):
        assert google.status_code == 200

    def test_html_title(self, google):
        soup = BeautifulSoup(google.content, "html.parser")
        assert soup.title.text.upper() == "GOOGLE"

Answer 1

Share same instance of object to all tests (or modular tests) using combination of conftest.py , fixtures and plain class

I'd like to share my solution, which comes from the Pytest documentation (7.2 currently)

Modularity: using fixtures from a fixture function

Now, if we combine it with a conftest.py this is what we could do: First having this structure (just to show sub-module and that, object is instanciated once for all tests)

├── conftest.py
├── sub_folder
│   ├── __init__.py
│   └── test_sub_1.py
├── test_1.py
├── test_2.py

This is the content conftest.py

"""tests/conftest.py"""
import pytest


class MockServer():
    def get(self, url):
        return "hello-world"

class App:
    def __init__(self, http_connection):
        print("APP CREATED")
        self.http_connection = http_connection

@pytest.fixture(scope="session")
def http_connection():
    print("HTTP_CONNECTION FIXTURE")
    return MockServer()

@pytest.fixture(scope="session")
def app(http_connection):
    print("CREATE APP")
    return App(http_connection)

tests/test_1.py

class TestClass1:

    def test_1(self, app):
        http_connection = app.http_connection

        assert http_connection.get("my-url") ==  "hello-world"

    def test_2(self, app):
        http_connection = app.http_connection

        assert http_connection.get("my-url") ==  "hello-world"

tests/test_2.py

class TestClass2:

    def test_1(self, app):
        http_connection = app.http_connection

        assert http_connection.get("my-url") ==  "hello-world"

    def test_2(self, app):
        http_connection = app.http_connection

        assert http_connection.get("my-url") ==  "hello-world"

tests/sub_folder/test_sub_1.py

"""tests/sub_folder/test_sub_1.py"""

class TestSubClass1:

    def test_sub_1(self, app):
        http_connection = app.http_connection

        assert http_connection.get("my-url") ==  "hello-world"

    def test_sub_2(self, app):
        http_connection = app.http_connection

        assert http_connection.get("my-url") ==  "hello-world"

Now, lets run

pytest -rP

The output should be something like

tests/test_1.py::TestClass1::test_1 PASSED                                                                                               [ 16%]
tests/test_1.py::TestClass1::test_2 PASSED                                                                                               [ 33%]
tests/test_2.py::TestClass2::test_1 PASSED                                                                                               [ 50%]
tests/test_2.py::TestClass2::test_2 PASSED                                                                                               [ 66%]
tests/sub_folder/test_sub_1.py::TestSubClass1::test_sub_1 PASSED                                                                         [ 83%]
tests/sub_folder/test_sub_1.py::TestSubClass1::test_sub_2 PASSED                                                                         [100%]

==================================================================== PASSES ====================================================================
______________________________________________________________ TestClass1.test_1 _______________________________________________________________
------------------------------------------------------------ Captured stdout setup -------------------------------------------------------------
HTTP_CONNECTION FIXTURE
CREATE APP
APP CREATED
============================================================== 6 passed in 0.23s ===============================================================

As you can see, by the output, (HTTP_CONNECTION FIXTURE, CREATE APP, APP CREATED) is run only once. That's good when we need to share reasource across all tests. Having said that, now let's combine it with hoefling answer, I only add tests/test_1.py

tests/test_1.py

"""tests/test_1.py"""
import pytest

class TestClass1:
    @pytest.fixture(autouse=True)
    def _app(self, app):
        self.app = app

    def test_1(self):
        assert self.app.http_connection.get("my-url") ==  "hello-world"

    def test_2(self):
        assert self.app.http_connection.get("my-url") ==  "hello-world"

That's already better, but we can take it a step further, let's have a Base test class and having our test inherit from it conftest.py

"""tests/conftest.py"""
import pytest


class MockServer():
    def get(self, url):
        return "hello-world"

class App:
    def __init__(self, http_connection):
        print("APP CREATED")
        self.http_connection = http_connection

@pytest.fixture(scope="session")
def http_connection():
    print("HTTP_CONNECTION FIXTURE")
    return MockServer()

@pytest.fixture(scope="session")
def app(http_connection):
    print("CREATE APP")
    return App(http_connection)


class Base:
    @pytest.fixture(autouse=True)
    def _app(self, app):
        self.app = app

Now """tests/test_1.py""" can look like

"""tests/test_1.py"""
from conftest import Base

class TestClass1(Base):

    def test_1(self):
        assert self.app.http_connection.get("my-url") ==  "hello-world"

    def test_2(self):
        assert self.app.http_connection.get("my-url") ==  "hello-world"

Answer 2

Sure, just use an autouse fixture. Here is the relevant spot in pytest docs. In your example, the change would be introducing an extra fixture (I named it _request_google_page):

from bs4 import BeautifulSoup
import pytest
import requests

@pytest.fixture()
def google():
    return requests.get("https://www.google.com")


class TestGoogle:

    @pytest.fixture(autouse=True)
    def _request_google_page(self, google):
        self._response = google

    def test_alive(self):
        assert self._response.status_code == 200

    def test_html_title(self):
        soup = BeautifulSoup(self._response.content, "html.parser")
        assert soup.title.text.upper() == "GOOGLE"

You could even drop the google fixture completely and move the code to _request_google_page:

@pytest.fixture(autouse=True)
def _request_google_page(self):
    self._response = requests.get("https://www.google.com")

Note that _request_google_page will be called once per test by default, so each test will get a new response. If you want the response to be initialized once and reused throughout all tests in the TestGoogle class, adjust the fixture scopes (scope='class' for _request_google_page and scope='module' or scope='session' for google). Example:

from bs4 import BeautifulSoup
import pytest
import requests


@pytest.fixture(scope='module')
def google():
    return requests.get("https://www.google.com")


@pytest.fixture(autouse=True, scope='class')
def _request_google_page(request, google):
    request.cls._response = google


class TestGoogle:

    def test_alive(self):
        assert self._response.status_code == 200

    def test_html_title(self):
        soup = BeautifulSoup(self._response.content, "html.parser")
        assert soup.title.text.upper() == "GOOGLE"

Answer 3

I had to solve a similar problem and the accepted solution didn't work for me with a class-scoped fixture.

I wanted to call a fixture once per test class and re-use the value in test methods using self. This is actually what the OP was intending to do as well.

You can use the request fixture to access the class that's using it (request.cls) and assign the fixture value in a class attribute. Then you can access this attribute from self. Here's the full snippet:

from bs4 import BeautifulSoup
import pytest
import requests

@pytest.fixture(scope="class")
def google(request):
    request.cls.google = requests.get("https://www.google.com")


@pytest.mark.usefixtures("google")
class TestGoogle:
    def test_alive(self):
        assert self.google.status_code == 200

    def test_html_title(self):
        soup = BeautifulSoup(self.google.content, "html.parser")
        assert soup.title.text.upper() == "GOOGLE"

Hope that helps anyone else coming to this question.