input: Write a python function to measure the successful pings per second.
  assert measure_pings_per_second("61:8E:9C:CD:03", 74) >= 0
  assert measure_pings_per_second("10:20:30:40:50", 10) >= 0
output: def measure_pings_per_second(mac_address, num_pings):
      import time
      import random
      
      def ping(mac_address):
          # Simulate a ping to the device with the given MAC address
          # For the purpose of this function, we simulate the success/failure of a ping
          return random.choice([True, False])
      
      successful_pings = 0
      start_time = time.time()
      
      for _ in range(num_pings):
          if ping(mac_address):
              successful_pings += 1
      
      end_time = time.time()
      elapsed_time = end_time - start_time
      
      if elapsed_time == 0:
          return 0  # Avoid division by zero
      
      return successful_pings / elapsed_time