Pytest fixture for a class through self not as method argument

Asked 2/5, 2018 at 10:42 Answered 22/3, 2023 at 8:40

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"

Copse answered 2/5, 2018 at 10:42 Comment(0)

107

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"

Bucket answered 2/5, 2018 at 12:47 Comment(14)

Thanks @Bucket That's what I wanted. I never understood the autouse fixture functionality. I understand now. Cheers. – Copse 3/5, 2018 at 14:22

Glad I could help you! – Bucket 4/5, 2018 at 13:10

@Bucket for some reason this never works for me. The test methods seem to be getting a new instance and self does not have the attributes in the setup method. Just for context, I'm using 2 pytext.mark... on the class. – Orchardist 15/1, 2019 at 3:25

@Orchardist best is to ask a separate question, including a minimal reproducible example of the failing test setup you have. Can you do that? – Bucket 15/1, 2019 at 8:6

@hoefling, sure. Please check this question. Though it is another issue there, but it has the description of this issue. #54193019 – Orchardist 15/1, 2019 at 9:27

@hoefling, When I set the scope _request_google_page to 'class' and the scope of google to "module", I see the following error inside the function "def test_alive(self):" AttributeError: 'TestGoogle' object has no attribute '_response' Any idea? – Combust 31/7, 2020 at 16:42

@PrashantPathak I have added a snippet with adjusted scopes at the end of the answer, check it out. It will work when you copy it as-is. – Bucket 31/7, 2020 at 17:55

@hoefling, Thanks, So it means the function should be outside the class scope. – Combust 1/8, 2020 at 14:59

@Bucket Can you also help me to understand one concept? which I am getting hard time to clear. So in the above code def _request_google_page() does not return anything still we are able to use response object in def test_alive(). So how the "request.cls._response" is getting accessed inside the class test methods, how is the call follow? – Combust 1/8, 2020 at 15:3

@PrashantPathak this is part of test collection and preparation. request.cls will be TestGoogle when the _request_google_page fixture is evaluated on test collection, so after TestGoogle is collected, TestGoogle._response will be initialized; after that, TestGoogle().test_alive() is executed and self._response is available. It's a class variable, actually. – Bucket 2/8, 2020 at 10:36

@hoefling, Ohh I see so this "self" here is not an instance variable it's basically pointing to the class variable. Got it now. Thanks for your clarification – Combust 5/8, 2020 at 15:26

I am facing another issue with it ScopeMismatch: You tried to access the 'function' scoped fixture with a 'class' scoped request object, involved factories – Rags 12/4, 2021 at 18:37

@Anuragjain this means you have broadened the scope in a chain of fixtures invocation, which isn't allowed. This is not an issue with the code in the answer; if you need help, ask a new question with a minimal reproducible example. – Bucket 12/4, 2021 at 19:19

The last example is horrendous. Please don't do this. Tests (well, all the code) should be easy to understand. Remember: "Explicit is better than implicit" – Islean 1/12, 2022 at 15:10

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.

Racine answered 23/7, 2020 at 5:50 Comment(4)

However there is not way to set the value of self.variable through this? – Ruppert 4/2, 2021 at 20:57

@Ruppert I don't think there is and I can't think of a case when it would be needed and cls wouldn't work – Racine 5/2, 2021 at 10:3

i actually want exactly this behaviour. set the value of the self.variable in a test and use that result in following tests – Buy 5/4, 2021 at 11:14

@JorritSmit sounds strange to set a value in one test to be used in other tests. A test should test not generate values for other tests. – Lyrist 14/5, 2021 at 17:38

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"

Concoction answered 22/3, 2023 at 8:40 Comment(0)

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

Modularity: using fixtures from a fixture function

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