A method of testing a plurality of devices, such as hard disk drives, in response to a random request by checking whether hard disk drive have been loaded, and sequentially allocating one test thread for each loaded hard disk drive. Each allocated thread performs a series of test job operations one by one when called and required for testing the loaded hard disk drive, and records a test status of each hard disk drive whenever one job operation of the test by the test thread is terminated to allow a next test thread to refer to the recorded test status. Each hard disk drive is tested according to a time required to test that hard disk drive.