If you're on pytest 3.0 or later, I think you should be able to solve this particular scenario by writing a fixture along the lines of:

@pytest.fixture(params=['dir1_fixture', 'dir2_fixture'])
def dirname(request):
    return request.getfixturevalue(request.param)

Docs here: http://doc.pytest.org/en/latest/builtin.html#_pytest.fixtures.FixtureRequest.getfixturevalue

However, you can't use this approach if the fixture you're attempting to dynamically load is parametrized.

Alternatively, you might be able to figure something out with the pytest_generate_tests hook. I haven't been able to bring myself to look into that much, though.

Will was on the right path, you should use request.getfixturevalue to retrieve the fixture.

But you can do it right in the test, which is simpler.

@pytest.mark.parametrize('dirname, expected', [
    ('dir1_fixture', 'expected1'),
    ('dir2_fixture', 'expected2')])
def test_directory_command(dirname, expected, request):
    result = my_package.directory_command(request.getfixturevalue(dirname))
    assert result == expected

Another way is to use lazy-fixture plugin:

@pytest.mark.parametrize('dirname, expected', [
    (pytest.lazy_fixture('dir1_fixture'), 'expected1'),
    (pytest.lazy_fixture('dir2_fixture'), 'expected2')])
def test_directory_command(dirname, expected):
    result = my_package.directory_command(dirname)
    assert result == expected

As for now, my only solution is to create a fixture that returns a dictionary of fixtures.

import pytest
import my_package

@pytest.fixture
def dir1_fixture():
    return '/dir1'

@pytest.fixture
def dir2_fixture():
    return '/dir2'

@pytest.fixture
def dir_fixtures(
    dir1_fixture,
    dir2_fixture
    ):
    return {
        'dir1_fixture': dir1_fixture,
        'dir2_fixture': dir2_fixture
    }

@pytest.mark.parametrize('fixture_name, expected', [('dir1_fixture', 'expected1'), ('dir2_fixture', 'expected2')]
def test_directory_command(dir_fixtures, fixture_name, expected):
    dirname = dir_fixtures[fixture_name]
    result = my_package.directory_command(dirname)
    assert result == expected

Not the best since it does not use a solution built into pytest, but it works for me.