The pilot was completing his multi-engine checkride with a Designated Pilot Examiner (DPE). The DPE had configured the airplane for a simulated single-engine landing. The DPE recalled the pilot calling out an extension of the landing gear, but the pilot did not remember putting the landing gear down and nor verifying that it was extended. Neither pilot nor DPE recalled hearing the landing gear position warning horn before touchdown. The airplane touched down on the runway with the landing gear retracted and slid down the runway on the underside of the fuselage, substantially damaging it. A postaccident examination of the landing gear system revealed that the landing gear position warning horn was functioning normally. Neither pilot reported that there were any preimpact mechanical malfunctions or failures with the airplane were reported that would have precluded normal operation.