pytest: optional parameter (https://github.com/jonparrott/nox/issues/62)

README.md

By default, the "extra" test is skipped:

$ py.test test.py -vv
================== test session starts ==================
platform linux -- Python 3.6.2, ...
cachedir: .../.cache
rootdir: ${ROOTDIR}, inifile: setup.cfg
plugins: cov-2.5.1
collected 3 items

test.py::test_it[40-42] PASSED
test.py::test_it[0-2] SKIPPED
test.py::test_too[11-12-23] PASSED

========== 2 passed, 1 skipped in 0.01 seconds ==========

However, if the flag to activate it is used, the second test is run:

$ py.test test.py --hey-you-guys -vv
================== test session starts ==================
platform linux -- Python 3.6.2, ...
cachedir: .../.cache
rootdir: ${ROOTDIR}, inifile: setup.cfg
plugins: cov-2.5.1
collected 4 items

test.py::test_it[40-42] PASSED
test.py::test_it[0-2] PASSED
test.py::test_too[11-12-23] PASSED
test.py::test_too[20-31.5-51.5] PASSED

================ 4 passed in 0.01 seconds ===============

Also note the "magical" appearance of a fourth test test_too[20-31.5-51.5]. This is due to a different approach than was used to skip test_it[0-2]. Instead of using a pytest.mark to skip the case, it was instead omitted from the cases passed to pytest.mark.parametrize.

conftest.py

def pytest_addoption(parser):
    parser.addoption(
        '--hey-you-guys',
        dest='hey_you_guys',
        action='store_false',
        help='Conditional inlcude.',
    )

test.py

import pytest


HEY_YOU_GUYS = pytest.config.getoption('--hey-you-guys')
HEY_MARK = pytest.mark.skipif(
    HEY_YOU_GUYS,
    reason='Conditional include requested.',
)
OPTIONS = [
    (11, 12, 23),
]
if not HEY_YOU_GUYS:
    OPTIONS.append(
        (20, 31.5, 51.5),
    )



def f(n):
    return n + 2


def g(x, y):
    return x + y


@pytest.mark.parametrize(
    'test_input,expected',
    [
        (40, 42),
        pytest.param(0, 2, marks=HEY_MARK),
    ]
)
def test_it(test_input, expected):
    assert f(test_input) == expected


@pytest.mark.parametrize('first,second,result', OPTIONS)
def test_too(first, second, result):
    assert g(first, second) == result