A memory card includes a memory cell, a connector, a controller, and firmware. The memory cell can switch between a plurality of states. The connector can be connected to an external device and exchange signals including commands and data with the external device. The controller exchanges signals with the connector, analyzes a received signal, and accesses the memory cell to record, retrieve or modify data based on the analysis result. The firmware is located within the controller, controls the operation of the controller, and can be set to a test mode or a user mode. When the firmware receives a test command from the external device and the firmware is set to the test mode, the firmware performs a defect test on the memory cell and transmits the result of the defect test to the external device through the connector.