A test method including executing a data transfer instruction with regard to transfer of data between a plurality of multiplexed storage devices and a plurality of main systems logically connected to the plurality of storage devices, storing an initial value of an operand upon execution of the data transfer instruction, re-setting the stored initial value to the operand upon occurrence of an interrupt triggered by an exception, and repeatedly executing the data transfer instruction and re-setting the stored initial value to the operand, by the main system accessing the storage device, until the data transfer instruction is completed normally.