py.test - idparametrize mark, to easily parametrize tests with test ids/test names

conftest.py

def pytest_generate_tests(metafunc):
    """
    If the test_ fn has a idparametrize mark, use it to create parametrized
    tests with ids. Instead of giving a list of argvals (test values), it
    should be a dict of test id strings -> tuple of test values
    e.g.
    @py.test.mark.idparametrize(('a', 'b'), {
        'foo': (1, 2),
        'bar': (3, 4),
    })
    Note tests will be ordered according to the test id string.
    """

    idparametrize = getattr(metafunc.function, 'idparametrize', None)
    if idparametrize:
        argnames, testdata = idparametrize.args
        ids, argvalues = zip(*sorted(testdata.items()))
        metafunc.parametrize(argnames, argvalues, ids=ids)

shell.txt

$py.test test_foo.py -k groupby -v

========= test session starts ===========
platform linux3 -- Python 2.7.2 -- pytest-2.2.3 -- (...)
collected 1111 items 

test_foo.py:1539: test_groupby[even sorted] PASSED
test_foo.py:1539: test_groupby[even unsorted] PASSED
test_foo.py:1539: test_groupby[under 5 sorted] PASSED

test_foo.py

# note I am using py.test 2.2.3, I think in later versions it would just be
# pytest.mark not py.test.mark


from itertools import groupby


@py.test.mark.idparametrize(('data', 'keyFn', 'expected'), {
    'even sorted': ([1, 3, 2, 4], lambda v: v % 2 == 0, [(False, [1, 3]),
                                                         (True, [2, 4])]),
    'even unsorted': ([1, 2, 3, 4], lambda v: v % 2 == 0, [(False, [1]),
                                                           (True, [2]),
                                                           (False, [3]),
                                                           (True, [4])]),
    'under 5 sorted': ([2, 4, 6, 8, 10, 12], lambda v: v < 5, [(True, [2, 4]),
                                                               (False, [6, 8, 10, 12])]),
})
def test_groupby(data, keyFn, expected):
    result = [(k, list(g)) for k, g in groupby(data, key=keyFn)]
    assert result == expected

conftest.py line 14 can be refactored to idparametrize = metafunc.definition.get_closest_marker('idparametrize'), which avoids the warning:

RemovedInPytest4Warning: MarkInfo objects are deprecated as they contain merged marks which are hard to deal with correctly.