@abc.abstractmethod<EOL><INDENT>def is_active(self):<DEDENT>
return<EOL>
Tests if this operable is active.

        ``is_active()`` is ``true`` if ``is_operational()`` is ``true``
        and ``is_disabled()`` is ``false,`` or ``is_enabled()`` is
        ``true``.

        :return: ``true`` if this operable is on, ``false`` if it is off
        :rtype: ``boolean``


        *compliance: mandatory -- This method must be implemented.*