'TestClient.test_constructor_w_implicit_inputs' unit test failure

[tseaver]

From this Kokoro build failure:

________________ TestClient.test_constructor_w_implicit_inputs _________________

self = <tests.unit.test_client.TestClient testMethod=test_constructor_w_implicit_inputs>

    def test_constructor_w_implicit_inputs(self):
        from google.cloud.datastore.client import _CLIENT_INFO
        from google.cloud.datastore.client import _DATASTORE_BASE_URL

        other = "other"
        creds = _make_credentials()

        klass = self._get_target_class()
        patch1 = mock.patch(
            "google.cloud.datastore.client._determine_default_project",
            return_value=other,
        )
        patch2 = mock.patch("google.auth.default", return_value=(creds, None))

        with patch1 as _determine_default_project:
            with patch2 as default:
                client = klass()

        self.assertEqual(client.project, other)
        self.assertIsNone(client.namespace)
        self.assertIs(client._credentials, creds)
        self.assertIs(client._client_info, _CLIENT_INFO)
        self.assertIsNone(client._http_internal)
        self.assertIsNone(client._client_options)
        self.assertEqual(client.base_url, _DATASTORE_BASE_URL)

        self.assertIsNone(client.current_batch)
        self.assertIsNone(client.current_transaction)

>       default.assert_called_once_with()

tests/unit/test_client.py:183:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
.nox/unit-2-7/lib/python2.7/site-packages/mock/mock.py:957: in assert_called_once_with
    return self.assert_called_with(*args, **kwargs)
.nox/unit-2-7/lib/python2.7/site-packages/mock/mock.py:944: in assert_called_with
    six.raise_from(AssertionError(_error_message(cause)), cause)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

value = AssertionError("expected call not found.\nExpected: default()\nActual: default(scopes=('https://www.googleapis.com/auth/datastore',))",)
from_value = None

    def raise_from(value, from_value):
>       raise value
E       AssertionError: expected call not found.
E       Expected: default()
E       Actual: default(scopes=('https://www.googleapis.com/auth/datastore',))