1. A method for testing a memory subsystem, comprising: inserting a detachable diagnostic memory module into a connector of the memory subsystem, wherein the connector is a connector for receiving an ordinary memory module by detachably and electrically coupling the diagnostic memory module to the memory subsystem by memory module interface terminals of the connector; communicating with the detachable diagnostic memory module to transfer diagnostic information between the detachable diagnostic memory module and an external diagnostic system wherein the diagnostic information includes a command received by the diagnostic memory module that alters an electrical behavior of the diagnostic memory module; and testing the memory subsystem by altering the electrical behavior of the detachable diagnostic memory module in response to the command.