A device testing apparatus, such as a hard disk drive (HDD) testing apparatus, using one host computer to test a plurality of the devices, such as to burn-in test HDDs. A host computer having at least two serial communication ports is communicably connected to power cards which supply operating power to each HDD to be tested. A serial communication exchanger is communicably connected to the serial communication ports of the host computer and to the HDDs, and responds to channel selection instructions issued by the host computer to selectively establish a serial communication channel among HDDs, the power card, and the host computer. The single host computer conducts the testing of the HDDs by communicating with the HDDs via the established serial communication channel.