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.

Answer 1

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