code: def testSetLengthAddSteps(self):
      poly_seq = polyphony_lib.PolyphonicSequence(steps_per_quarter=1)
      poly_seq.set_length(5)
  
      self.assertEqual(5, poly_seq.num_steps)
      self.assertListEqual([0, 0, 1, 2, 3, 4, 5], poly_seq.steps)
  
      pe = polyphony_lib.PolyphonicEvent
      poly_events = [
          pe(pe.START, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.END, None),
      ]
      self.assertEqual(poly_events, list(poly_seq))
  
      # Add 5 more steps to make sure END is managed properly.
      poly_seq.set_length(10)
  
      self.assertEqual(10, poly_seq.num_steps)
      self.assertListEqual(
          [0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10], poly_seq.steps
      )
  
      pe = polyphony_lib.PolyphonicEvent
      poly_events = [
          pe(pe.START, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.STEP_END, None),
          pe(pe.END, None),
      ]
      self.assertEqual(poly_events, list(poly_seq))
  
imports: import copy
  from magenta.common import testing_lib
  from magenta.models.polyphony_rnn import polyphony_lib
  from note_seq import sequences_lib
  from note_seq import testing_lib
  from note_seq.protobuf import music_pb2
  import tensorflow.compat.v1
label_desc: Use image node_id 10 for calling the PolyphonyLibTest obj's underlying member method code with example usage: obj.testSetLengthAddSteps() without return types