MongoDB 3.7 has new expectations around how users are created that is causing our tests to fail. We'll make changes to PyMongo itself to work with the server changes in the next feature release. For now, change the test suite to create and drop users using the createUser and dropUser commands directly, except when explicitly testing Database.add_user and Database.remove_user. We were going to have to make these changes eventually when removing add_user and remove_user (which are deprecated). MongoDB 3.7 is just moving up the timeline.