How send a config variable to a py.test test?

Question

I have a test suite which needs to run with multiple backends. It isn't a simple parameterized test though since it applies to the whole suite (multiple files/modules). I can control the run via the environment, but I'm wondering if py.test has a clearer way to express this.

That is, I'm looking for something like this:

py.test --set-mode ALPHA

Then in my test I would read this value:

if py.test.mode == 'ALPHA':

Answer 1

Using pytest_addoption:

test_blah.py

def test_something(mode):
    if mode == 'ALPHA':
        assert True
    else:
        assert False

conftest.py

import pytest

def pytest_addoption(parser):
    parser.addoption("--set-mode", action="store", default="ALPHA",
                                help="ALPHA or BETA")

@pytest.fixture
def mode(request):
    return request.config.getoption("--set-mode")

See Pass different values to a test function, depending on command line options.