Test Utils - _wait_for_srouter_slaves_endpoints - unclear failure

    @retrying.retry(wait_fixed=2000,
                    retry_on_result=lambda r: r is False,
                    retry_on_exception=lambda _: False)
    def _wait_for_srouter_slaves_endpoints(self):
        # Get currently known agents. This request is served straight from
        # Mesos (no AdminRouter-based caching is involved).
        r = self.get('/mesos/master/slaves')
        assert r.status_code == 200
    
        data = r.json()
        # only check against the slaves we expect to be in the cluster
        # so we can check that cluster has returned after a failure
        # in which case will will have new slaves and dead slaves
        slaves_ids = sorted(x['id'] for x in data['slaves'] if x['hostname'] in self.all_slaves)
    
        for slave_id in slaves_ids:
            # AdminRouter's slave endpoint internally uses cached Mesos
            # state data. That is, slave IDs of just recently joined
            # slaves can be unknown here. For those, this endpoint
            # returns a 404. Retry in this case, until this endpoint
            # is confirmed to work for all known agents.
            uri = '/slave/{}/slave%281%29/state'.format(slave_id)
            r = self.get(uri)
            if r.status_code == 404:
                return False
>           assert r.status_code == 200
E           AssertionError

        assert r.status_code == 200, "Expecting status code 200 for Metronome but got {} with body {}"\
            .format(r.status_code, r.content)