old_contents: 
  class TestTuringCa(object):
      def test_turing_main(self):
          from zasim.examples.turing.main import main
          main()
  
  
new_contents: from zasim.examples.turing import main
  
  class TestTuringCa(object):
      def test_turing_main(self):
          main.main()
  
      def test_turing_step(self):
          tape = main.TuringTapeSimulator()
          start_conf = tape.get_config().copy()
          tape.step()
          end_conf = tape.get_config().copy()
  
          for index in range(tape.shape[0] - 1):
              # if there's a signal in the field now, the data in the signal
              # will have been in the top half of the field in the previous
              # step.
              if end_conf[index] % 4 != 3:
                  assert end_conf[index] % 4 == start_conf[index] / 4
  
  
subject: check the correctness of the turing example a bit.