The engine was started and stabilized at idle RPM for approximately 3 minutes while the initial leak check was performed by the two journeymen mechanics that were working around the engine. One of these two mechanics then called the captain on the ground intercom system and reported that a small oil leak was detected, and he requested that the captain run the engine at 70 percent power for 2 minutes to conduct further checks. The captain complied with the request, after verifying with the mechanic that the area around the airplane was clear. Witnesses on the ground and in the airplane stated that they saw the mechanic on the outboard side of the engine stand up, step into the inlet hazard zone, and become ingested into the intake of the engine. This occurred about 90 seconds into the 70-percent-power engine run. The mechanic was not wearing any type of safety equipment or lanyard to prevent the ingestion. Upon sensing a buffet, the captain immediately retarded the power lever back to the idle position. The first officer stated to the captain that something went into the engine and the captain immediately cut off the start lever to stop the engine run.