TASK: Start a shell command 'sleep 100' asynchronously. Verify it is running using its PID, then terminate it using process_terminate. Finally, you MUST call write_file to save the exact string 'terminated successfully' to 'termination_verify.txt'.
The sleep process was started asynchronously, verified to be running, then terminated successfully. The confirmation message has been saved to 'termination_verify.txt'.