How to run a method before all tests in all classes?

Question

I'm writing selenium tests, with a set of classes, each class containing several tests. Each class currently opens and then closes Firefox, which has two consequences:

• super slow, opening firefox takes longer than running the test in a class...
• crashes, because after firefox has been closed, trying to reopen it really quickly, from selenium, results in an 'Error 54'

I could solve the error 54, probably, by adding a sleep, but it would still be super slow.

So, what I'd like to do is reuse the same Firefox instances across all test classes. Which means I need to run a method before all test classes, and another method after all test classes. So, 'setup_class' and 'teardown_class' are not sufficient.

Solution 1

You might want to use a session-scoped "autouse" fixture:

# content of conftest.py or a tests file (e.g. in your tests or root directory)

@pytest.fixture(scope="session", autouse=True)
def do_something(request):
    # prepare something ahead of all tests
    request.addfinalizer(finalizer_function)

This will run ahead of all tests. The finalizer will be called after the last test finished.

Solution 2

Using session fixture as suggested by hpk42 is great solution for many cases, but fixture will run only after all tests are collected.

Here are two more solutions:

conftest hooks

Write a pytest_configure or pytest_sessionstart hook in your conftest.py file:

# content of conftest.py


def pytest_configure(config):
    """
    Allows plugins and conftest files to perform initial configuration.
    This hook is called for every plugin and initial conftest
    file after command line options have been parsed.
    """


def pytest_sessionstart(session):
    """
    Called after the Session object has been created and
    before performing collection and entering the run test loop.
    """


def pytest_sessionfinish(session, exitstatus):
    """
    Called after whole test run finished, right before
    returning the exit status to the system.
    """


def pytest_unconfigure(config):
    """
    called before test process is exited.
    """

pytest plugin

Create a pytest plugin with pytest_configure and pytest_unconfigure hooks.
Enable your plugin in conftest.py:

# content of conftest.py

pytest_plugins = [
    'plugins.example_plugin',
]


# content of plugins/example_plugin.py
def pytest_configure(config):
    pass


def pytest_unconfigure(config):
    pass

Solution 3

Starting from version 2.10 there is a cleaner way to tear down the fixture as well as defining its scope. So you may use this syntax:

@pytest.fixture(scope="module", autouse=True)
def my_fixture():
    print ('INITIALIZATION')
    yield param
    print ('TEAR DOWN')

The autouse parameter: From documentation:

Here is how autouse fixtures work in other scopes:

• autouse fixtures obey the scope= keyword-argument: if an autouse fixture has scope='session' it will only be run once, no matter where it is defined. scope='class' means it will be run once per class, etc.

• if an autouse fixture is defined in a test module, all its test functions automatically use it.

• if an autouse fixture is defined in a conftest.py file then all tests in all test modules below its directory will invoke the fixture.

  ...

The "request" parameter: Note that the "request" parameter is not necessary for your purpose although you might want to use it for other purposes. From documentation:

"Fixture function can accept the request object to introspect the “requesting” test function, class or module context.."

Solution 4

Try to use pytest_sessionstart(session) in conftest.py

Example:

# project/tests/conftest.py

def pytest_sessionstart(session):
    print('BEFORE')

# project/tests/tests_example/test_sessionstart.py

import pytest


@pytest.fixture(scope='module', autouse=True)
def fixture():
    print('FIXTURE')


def test_sessonstart():
    print('TEST')

Log:

BEFORE
============================================================================ test session starts =============================================================================
platform darwin -- Python 3.7.0, pytest-5.4.1, py-1.8.1, pluggy-0.13.1 -- /Library/Frameworks/Python.framework/Versions/3.7/bin/python3
cachedir: .pytest_cache
rootdir: /Users/user/Documents/test, inifile: pytest.ini
plugins: allure-pytest-2.8.12, env-0.6.2
collected 1 item                                                                                                                                                             

tests/6.1/test_sessionstart.py::test_sessonstart FIXTURE
TEST
PASSED

Read more here: https://docs.pytest.org/en/latest/reference.html#_pytest.hookspec.pytest_sessionstart

View more solutions

Comments

[Math is Hard]

This is the best answer. Put a conftest.py in the same directory as your other tests that you wish to run with the same pytest_sessionstart and pytest_sessionfinish routines.

[lalatnayak]

I think this does not work if the tests are spread across multiple files

[machazthegamer]

This won't work if i want to include a function scoped fixture to be used in this function

[Scott McAllister]

This absolutely works when tests are split across many files.

[Asclepius]

Will this run before each test or a total of once before testing?

[afaulconbridge]

This will be called once for each worker, if running tests in parallel. That might be what you want, or it might not be (e.g. a shared resource such as Firefox or a database).