import pytest
def pytest_addoption(parser):
    parser.addoption("-E", action="store", metavar="NAME",
        help="only run tests matching the environment NAME.")

def pytest_configure(config):
    # register an additional marker
    config.addinivalue_line("markers",
        "env(name): mark test to run only on named environment")

def pytest_runtest_setup(item):
    envnames = [mark.args[0] for mark in item.iter_markers(name='env')]
    if envnames:
        if item.config.getoption("-E") not in envnames:
            pytest.skip("test requires env in %r" % envnames)