[PYTHON] Make fixture an argument to parameterize in py.test

Introduction

The pytest fixture is a very useful tool when you want to repeat the test under the same conditions. When I wanted to use fixture as a test parameter to write a test that is common to various conditions, the information was unexpectedly not gathered on the net, so I will describe it here.

By the way, for information on how to use fixture as a test parameter, see Official Page and GitHub. / pytest-dev / pytest / issues / 349), so it's possible that a slightly easier way will be offered in the near future.

Thing you want to do

import pytest

@pytest.fixture
def fixture_a():
    yield 1

@pytest.fixture
def fixture_b():
    yield 2

@pytest.fixture
def fixture_c():
    yield 3

@pytest.mark.parametrize("expected, generated", [
        (1, fixture_a),
        (2, fixture_b),
        (5, fixture_c),
])
def test_fail(expected, generated):
    assert expected == generated

However, this doesn't work.

Alternative

Put together fixtures by using the decorator pytest.fixture.

test.py

#Other functions are the same as above

@pytest.fixture(params=['a', 'b', 'c'])
def context(request):
    if request.param == 'a':
        return (1, request.getfixturevalue('fixture_a'))
    elif request.param == 'b':
        return (2, request.getfixturevalue('fixture_b'))
    elif request.param == 'c':
        return (4, request.getfixturevalue('fixture_c'))

def test_fixture_parameterize(context):
    expected, generated = context
    assert expected == generated

$ pytest test.py
========================================= test session starts =========================================
platform linux2 -- Python 2.7.12, pytest-3.1.0, py-1.4.33, pluggy-0.4.0
rootdir: /home/koreyou/work/pytest_fixture_parameterize, inifile:
collected 3 items 

test.py ..F

============================================== FAILURES ===============================================
____________________________________ test_fixture_parameterize[c] _____________________________________

context = (4, 3)

    def test_fixture_parameterize(context):
        expected, generated = context
>       assert expected == generated
E       assert 4 == 3

test.py:31: AssertionError
================================= 1 failed, 2 passed in 0.02 seconds ==================================

It fails as expected.