Motor already uses doctest to test various documentation examples: https://evergreen.mongodb.com/task/motor_doctests_doctest_0e729fb6f3bc84a995233b21429cfc4ac30f73b7_21_02_12_19_32_37

However, many documentation examples do not use doctest and are likely incorrect. For example: 

• https://github.com/mongodb/motor/pull/101 AsyncIOMotorGridFSBucket.new_file() does not exist
• MOTOR-674 Wrong return values in example of open_upload_stream_with_id