def METHOD_NAME(self, env):
    """Set dummy environment variables for testing.
    Parameters
    ----------
    env : :class:`dict`
        Mapping of variables to values
    """
    from os import environ
    for k in env:
        if k in environ:
            self.environ_cache[k] = environ[k]
        else:
            self.environ_cache[k] = None
        environ[k] = env[k]
    return