python - How to skip a pytest using an external fixture?

Question

Background

I am running a py.test with a fixture in a conftest file. You can see the code below(this all works fine):

example_test.py

import pytest

@pytest.fixture
def platform():
    return "ios"

@pytest.mark.skipif("platform == 'ios'")
def test_ios(platform):
    if platform != 'ios':
        raise Exception('not ios')

def test_android_external(platform_external):
    if platform_external != 'android':
        raise Exception('not android')

conftest.py

import pytest

@pytest.fixture
def platform_external():
    return "android"

Problem

Now I want to be able to skip some tests that do not apply to my current test-run. In my example I am running tests either for iOS or Android (This is just for demonstration purposes only and could be any other expression).

Unfortunately I cannot get ahold of (my externally defined fixture) platform_external in the skipif statement. When I run the code below I receive the following exception: NameError: name 'platform_external' is not defined. I don't know if this is a py.test bug as locally defined fixtures are working.

add-on for example_test.py

@pytest.mark.skipif("platform_external == 'android'")
def test_android(platform_external):
    """This test will fail as 'platform_external' is not available in the decorator.
    It is only available for the function parameter."""
    if platform_external != 'android':
        raise Exception('not android')

So I thought I will just create my own decorator, just to see that it won't receive the fixtures as parameters:

from functools import wraps

def platform_custom_decorator(func):
    @wraps(func)
    def func_wrapper(*args, **kwargs):
        return func(*args, **kwargs)
    return func_wrapper

@platform_custom_decorator
def test_android_2(platform_external):
    """This test will also fail as 'platform_external' will not be given to the 
    decorator."""
    if platform_external != 'android':
        raise Exception('not android')

Question

How can I define a fixture in a conftest file and use it to (conditionally) skip a test?

Answer 1

It seems py.test doesn't use the test fixtures when evaluating the expression for skipif. By your example, test_ios is actually successful because it is comparing the function platform found in the module's namespace to the "ios" string, which evaluates to False hence the test is executed and succeeds. If pytest was inserting the fixture for evaluation as you expect, that test should have been skipped.

A solution to your problem (not to your question though) would be to implement a fixture that inspects marks into the tests, and skips them accordingly:

# conftest.py
import pytest

@pytest.fixture
def platform():
    return "ios"

@pytest.fixture(autouse=True)
def skip_by_platform(request, platform):
    if request.node.get_closest_marker('skip_platform'):
        if request.node.get_closest_marker('skip_platform').args[0] == platform:
            pytest.skip('skipped on this platform: {}'.format(platform))   

A key point is the autouse parameter, which would make that fixture to be automatically included by all tests. Then your tests can mark which platforms to skip like this:

@pytest.mark.skip_platform('ios')
def test_ios(platform, request):
    assert 0, 'should be skipped' 

Hope that helps!