Pytest 和动态夹具模块

Question

I am writing functional tests using pytest for a software that can run locally and in the cloud. I want to create 2 modules, each with the same module/fixture names, and have pytest load one or the other depending if I'm running tests locally or in the cloud:

/fixtures
/fixtures/__init__.py
/fixtures/local_hybrids
/fixtures/local_hybrids/__init__.py
/fixtures/local_hybrids/foo.py
/fixtures/cloud_hybrids
/fixtures/cloud_hybrids/__init__.py
/fixtures/cloud_hybrids/foo.py
/test_hybrids/test_hybrids.py

foo.py (both of them):

import pytest
@pytest.fixture()
def my_fixture():
    return True

/fixtures/__init__.py :

if True:
    import local_hybrids as hybrids
else:
    import cloud_hybrids as hybrids

/test_hybrids/test_hybrids.py :

from fixtures.hybrids.foo import my_fixture

def test_hybrid(my_fixture):
   assert my_fixture

The last code block doesn't work of course, because import fixtures.hybrids is looking at the file system instead of __init__.py 's "fake" namespace, which isn't like from fixtures import hybrids , which works (but then you cannot use the fixtures as the names would involve dot notation).

I realize that I could play with pytest_generate_test to alter the fixture dynamically (maybe?) but I'd really hate managing each fixture manually from within that function... I was hoping the dynamic import (if x, import this, else import that) was standard Python, unfortunately it clashes with the fixtures mechanism:

import fixtures
def test(fixtures.hybrids.my_fixture):  # of course it doesn't work :)
    ...

I could also import each fixture function one after the other in init; more legwork, but still a viable option to fool pytest and get fixture names without dots.

Show me the black magic. :) Can it be done?

Answer 1

I think in your case it's better to define a fixture - environment or other nice name.

This fixture can be just a getter from os.environ['KEY'] or you can add custom command line argument like here then use it like here and the final use is here .

What im trying to tell is that you need to switch thinking into dependency injection: everything should be a fixture. In your case (and in my plugin as well), runtime environment should be a fixture, which is checked in all other fixtures which depend on the environment.

Answer 2

You might be missing something here: If you want to re-use those fixtures you need to say it explicitly:

from fixtures.hybrids.foo import my_fixture

@pytest.mark.usefixtures('my_fixture')
def test_hybrid(my_fixture):
    assert my_fixture

In that case you could tweak pytest as following:

from local_hybrids import local_hybrids_fixture
from cloud_hybrids import cloud_hybrids_fixture

fixtures_to_test = {
    "local":None,
    "cloud":None
}

@pytest.mark.usefixtures("local_hybrids_fixture")
def test_add_local_fixture(local_hybrids_fixture):
    fixtures_to_test["local"] = local_hybrids_fixture

@pytest.mark.usefixtures("cloud_hybrids_fixture")
def test_add_local_fixture(cloud_hybrids_fixture):
    fixtures_to_test["cloud"] = cloud_hybrids_fixture

def test_on_fixtures():
    if cloud_enabled:
        fixture = fixtures_to_test["cloud"]
    else:
        fixture = fixtures_to_test["local"]
    ...

If there are better solutions around I am also interested;)

Answer 3

I don't really think there is a "good way" of doing that in python, but still it is possible with a little amount of hacking. You can update sys.path for the subfolder with fixtures you would like to use and import fixtures directly. In dirty case it look's like that:

for your fixtures/__init__.py:

if True:
    import local as hybrids
else:
    import cloud as hybrids

def update_path(module):
    from sys import path
    from os.path import join, pardir, abspath
    mod_dir = abspath(join(module.__file__, pardir))
    path.insert(0, mod_dir)

update_path(hybrids)

and in the client code (test_hybrids/test_hybrids.py):

import fixtures
from foo import spam

spam()

In other cases you can use much more complex actions to perform a fake-move of all modules/packages/functions etc from your cloud/local folder directly into the fixture's __init__.py. Still, I think - it does not worth a try.

One more thing - black magic is not the best thing to use, I would recommend you to use a dotted notation with "import X from Y" - this is much more stable solution.

Answer 4

Use the pytest plugins feature and put your fixtures in separate modules. Then at runtime select which plug-in you'll be drawing from via a command line argument or an environment variable. It needs to be something global because you need to place different pytest_plugins list assignments based on the global value.

Take a look at the section Conditional Plugins from this repo https://github.com/jxramos/pytest_behavior/tree/main/conditional_plugins