This happens with a standalone mongod or mongos, neither of which return a lastWrite document from ismaster.
====================================================================== FAIL: test_last_write_date (test_max_staleness.TestMaxStaleness) ---------------------------------------------------------------------- Traceback (most recent call last): File "/mnt/jenkins/workspace/mongo-python-driver-nightly/extensions/with-extensions/label/linux64/mongodb_configuration/single_server/mongodb_option/noauth/mongodb_server/master-nightly/python_language_version/2.7/test/__init__.py", line 324, in wrap return f(*args, **kwargs) File "/mnt/jenkins/workspace/mongo-python-driver-nightly/extensions/with-extensions/label/linux64/mongodb_configuration/single_server/mongodb_option/noauth/mongodb_server/master-nightly/python_language_version/2.7/test/test_max_staleness.py", line 290, in test_last_write_date self.assertTrue(last_write) AssertionError: None is not true