new_contents: import unittest
  import canopen
  
  
  class TestSync(unittest.TestCase):
  
      def test_sync_producer(self):
          network = canopen.Network()
          network.connect(bustype="virtual", receive_own_messages=True)
          producer = canopen.sync.SyncProducer(network)
          producer.transmit()
          msg = network.bus.recv(1)
          network.disconnect()
          self.assertEqual(msg.arbitration_id, 0x80)
          self.assertEqual(msg.dlc, 0)
  
      def test_sync_producer_counter(self):
          network = canopen.Network()
          network.connect(bustype="virtual", receive_own_messages=True)
          producer = canopen.sync.SyncProducer(network)
          producer.transmit(2)
          msg = network.bus.recv(1)
          network.disconnect()
          self.assertEqual(msg.arbitration_id, 0x80)
          self.assertEqual(msg.dlc, 1)
          self.assertEqual(msg.data, b"\x02")
  
  if __name__ == "__main__":
      unittest.main()
  
subject: Add unit test for SYNC producer