self = 
def test_from_pb_non_empty(self):
    from google.iam.v1 import policy_pb2
    from google.cloud.bigtable.policy import BIGTABLE_ADMIN_ROLE

    ETAG = b"ETAG"
    VERSION = 1
    members = ["serviceAccount:service_acc1@test.com", "user:user1@test.com"]
    empty = frozenset()
    message = policy_pb2.Policy(
        etag=ETAG,
        version=VERSION,
        bindings=[{"role": BIGTABLE_ADMIN_ROLE, "members": members}],
    )
    klass = self._get_target_class()
    policy = klass.from_pb(message)
    self.assertEqual(policy.etag, ETAG)
    self.assertEqual(policy.version, VERSION)
    self.assertEqual(policy.bigtable_admins, set(members))
    self.assertEqual(policy.bigtable_readers, empty)
    self.assertEqual(policy.bigtable_users, empty)
    self.assertEqual(policy.bigtable_viewers, empty)


  self.assertEqual(len(policy), 1)


E       AssertionError: 4 != 1
tests/unit/test_policy.py:127: AssertionError