Using fixtures in pytest.mark.parametrize

Originally reported by: Florian Rathgeber (BitBucket: frathgeber, GitHub: frathgeber)

I often have a use case like the following contrived example:

@pytest.fixture
def a():
    return 'a'

@pytest.fixture
def b():
    return 'b'

@pytest.mark.parametrize('arg', [a, b])
def test_foo(arg):
    assert len(arg) == 1

This doesn't currently do what's intended i.e. arg inside the test function is not the fixture value but the fixture function.

I can work around it by introducing a "meta fixture", but that's rather ugly:

@pytest.fixture(params=['a', 'b'])
def arg(request, a, b):
    return {'a': a, 'b': b}[request.param]

def test_foo(arg):
    assert len(arg) == 1

It would be convenient if a syntax like in the first case was supported.

• Bitbucket: https://bitbucket.org/pytest-dev/pytest/issue/349

Start by reading pytest.mark.parametrize and the fixture-resolution behavior shown in the examples. The work is done when parametrization can supply fixture values rather than fixture functions, with tests covering the a and b example and the existing meta-fixture behavior preserved.