'Test config file with enviroment variable.'

def test_enviroment_variable(self):

    os.environ['PASSWORD'] = 'secret_password'
    conf = 'password:    !env_var    PASSWORD'
    with io.StringIO(conf) as file:
        doc = yaml.yaml.safe_load(file)
    assert (doc['password'] == 'secret_password')
    del os.environ['PASSWORD']
