pytest: Using a "session" scope fixture along with default scope fixtures

Question

I'm building a pytest test suite, testing a package I'm building. The tests should verify some things about the pkg, such as minor functionality checks, minor sanity checks and so on. Some of the checks are done pre-install and some post-install (example code):

Tests file:

import pytest

class PreInstallTests(object):
    def test_foo(self, bar):
        assert bar > 2

class PostInstallTests(object):
    def test_goo(self, baz):
        assert baz < 3

    def test_hoo(self, baz):
        assert baz > 1

conftest file:

import pytest
@pytest.fixture
def tmp_dir():
    os.mkdir('tmp')
    yield
    shutil.rmtree('tmp')

@pytest.fixture
def bar(tmp_dir):
    yield 3

@pytest.fixture
def baz(install, tmp_dir):
    yield 2

@pytest.fixture(scope='session')
def install():
    # installs the pkg... (takes a lot of time)

As can be seen here, I have 2 post-install tests, each one using a fixture called baz that uses the install fixture. I want to have only one installation, and either use the same installation for all post-install-tests (not ideal, but the tests are minimal, and I don't want to waste much time on re-installing currently).

Using the "scope" session parameter can solve my problem, but that would prohibit me from using any other fixture, such as "tmp_dir" (which represents a fixture that I need, and must stay default-scoped...)

How can I achieve one install for all tests, and still use my other fixtures, whom I want to leave with their default scope?

I thought of making the install an autouse fixture, but I actually need it to be called after some of the other fixtures that are currently default scoped, and should stay that way

Using the "scope" session parameter can solve my problem, but that would prohibit me from using any other fixture, such as "tmp_dir" - you mean, prohibit using tmp_dir in install? Other than that (and wrong placed scope parameter in the install fixture), I don't see any issues with your code. — hoefling
You can always introduce another fixture, like e.g. real_install which is session-scoped, and change install to smth like def install(tmp_dir, real_install): return real_install with the default function scope. This way, the installation will still run once and you can combine its result with function-scoped fixtures. — hoefling
@hoefling For your 1st comment - yes, but I actually have a lot of fixtures like that one.. For your 2nd - thought about it, but that would make me change a lot of my fixtures into function calls (e.g. I have a fixture that shows the path of the pkg - so that would have to be a call to function) — CIsForCookies
@CIsForCookies, do you mean to say you want to use tmp_dir and many such function scoped fixtures in install fixture? Or you just want them be called before the install fixture. — yeniv

Gabriel Cappelli Gabriel Cappelli · Accepted Answer · 2019-09-17T23:44:59

Only solution I could think of is to have a flag controlling if you've already run the installation code, then keep the fixture with default scope.


import pytest

installed = False

@pytest.fixture()
def install():
    global installed
    if not installed:
        print('installing')
        installed = True

pytest: Using a "session" scope fixture along with default scope fixtures

2 Answers