Test if code is executed from within a py.test session

Question

I’d like to connect to a different database if my code is running under py.test. Is there a function to call or an environment variable that I can test that will tell me if I’m running under a py.test session? What’s the best way to handle this?

Asked By: Laizer

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Answer 1

A solution came from RTFM, although not in an obvious place. The manual also had an error in code, corrected below.

Detect if running from within a pytest run

Usually it is a bad idea to make application code behave differently
if called from a test. But if you absolutely must find out if your
application code is running from a test you can do something like
this:
# content of conftest.py
def pytest_configure(config):
    import sys
    sys._called_from_test = True

def pytest_unconfigure(config):
    import sys  # This was missing from the manual
    del sys._called_from_test
and then check for the sys._called_from_test flag:
if hasattr(sys, '_called_from_test'):
    # called from within a test run
else:
    # called "normally"
accordingly in your application. It’s also a good idea to use your own
application module rather than sys for handling flag.

Answered By: Laizer

Answer 2

While the hack explained in the other answer (http://pytest.org/latest/example/simple.html#detect-if-running-from-within-a-pytest-run) does indeed work, you could probably design the code in such a way you would not need to do this.

If you design the code to take the database to connect to as an argument somehow, via a connection or something else, then you can simply inject a different argument when you’re running the tests then when the application drives this. Your code will end up with less global state and more modulare and reusable. So to me it sounds like an example where testing drives you to design the code better.

Answered By: flub

Answer 3

A simpler solution I came to:

import sys

if "pytest" in sys.modules:
    ...

Pytest runner will always load the pytest module, making it available in sys.modules.

Of course, this solution only works if the code you’re trying to test does not use pytest itself.

Answered By: ramnes

Answer 4

Working with pytest==4.3.1 the methods above failed, so I just went old school and checked with:

script_name = os.path.basename(sys.argv[0])
if script_name in ['pytest', 'py.test']:
  print('Running with pytest!')

Answered By: duhaime

Answer 5

This could be done by setting an environment variable inside the testing code. For example, given a project

conftest.py
mypkg/
    __init__.py
    app.py
tests/
    test_app.py

In test_app.py you can add

import os
os.environ['PYTEST_RUNNING'] = 'true'

And then you can check inside app.py:

import os
if os.environ.get('PYTEST_RUNNING', '') == 'true':
    print('pytest is running')

Answered By: Alex

Answer 6

There’s also another way documented in the manual:
https://docs.pytest.org/en/latest/example/simple.html#pytest-current-test-environment-variable

Pytest will set the following environment variable PYTEST_CURRENT_TEST.

Checking the existence of said variable should reliably allow one to detect if code is being executed from within the umbrella of pytest.

import os
if "PYTEST_CURRENT_TEST" in os.environ:
    # We are running under pytest, act accordingly...

Answered By: cgons

Test if code is executed from within a py.test session

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