According to the pilot, the purpose of the flight was to complete a commercial single-engine land checkride with a designated pilot examiner. During the straight in landing approach, the pilot selected full flaps and reduced the engine power to idle in order to descend, but did not use the before landing checklist and did not extend the landing gear. Over the runway threshold, the pilot verified the throttle was at idle and began to flare the airplane. Prior to landing, the designated pilot examiner did not verify that the landing gear was extended. Subsequently, the airplane landed on the runway without the landing gear extended which resulted in substantial damage to the airframe. Both pilots reported that they did not hear the landing gear warning horn prior to landing without the landing gear extended. According to a mechanic, during the recovery of the airplane, when the battery switch was turned on, the landing gear warning horn sounded. The pilot reported no preimpact mechanical malfunctions or failures with the airplane that would have precluded normal operation. In addition, pilot noted that the before landing checklist was not completed and the accident could have been prevented if it had been completed.