code: def testVocabSize(self):
      encoder = music_encoders.MidiPerformanceEncoder(
          steps_per_second=100,
          num_velocity_bins=32,
          min_pitch=21,
          max_pitch=108,
      )
      self.assertEqual(310, encoder.vocab_size)
  
imports: import tempfile
  from magenta.models.score2perf import music_encoders
  import note_seq
  from note_seq import testing_lib
  import tensorflow.compat.v1
label_desc: Use image node_id 9 for calling the MidiPerformanceEncoderTest obj's underlying member method code with example usage: obj.testVocabSize() without return types