def add_template(endpoint_template):
    """
        Add a new template for the external API.

        :param six.text_type endpoint_template: a :obj:`IEndpointTemplate` to add to the
            :obj:`IExternalAPIMock` instance
        :raises: ValueError if the endpoint template has already been added
        :raises: TypeError if the endpoint template does not implement
            the expected interface (IEndpointTempalte)
        """
