code: def test_default_step(self):
      try:
          tf2.summary.experimental.set_step(333)
          # TODO(nickfelt): change test logic so we can just omit `step` entirely.
          event = self.histogram_event("a", [], step=None)
          self.assertEqual(333, event.step)
      finally:
          # Reset to default state for other tests.
          tf2.summary.experimental.set_step(None)
  
imports: import glob
  import os
  import numpy
  import tensorflow
  from tensorboard.compat import tf2
  from tensorboard.compat.proto import summary_pb2
  from tensorboard.plugins.histogram import metadata
  from tensorboard.plugins.histogram import summary
  from tensorboard.util import tensor_util
label_desc: Use image node_id 9 for calling the SummaryV3OpTest obj's underlying member method code with example usage: obj.test_default_step() without return types