def path_for_host(host, environ=None):
    if environ is None:
        environ = os.environ
    for kv_pair in environ['MOCK_SSH_ROOTS'].split(':'):
        this_host, this_path = kv_pair.split('=')
        if this_host == host:
            return os.path.abspath(this_path)
    raise KeyError('Host %s is not specified in $MOCK_SSH_ROOTS (%s)' %
                   (host, environ['MOCK_SSH_ROOTS']))
Check that changes are possible and sticky
dataset/ETHPy150Open Yelp/mrjob/tests/mockssh.py/path_for_host--crossover with--dataset/ETHPy150Open ellisonbg/altair/altair/tests/test_api.py/test_vl_spec_for_font_changes