docstr: Test that file version event does not trigger data purge.
code: def testOnlySummaryEventsTriggerDiscards(self):
      """Test that file version event does not trigger data purge."""
      gen = _EventGenerator(self)
      acc = ea.EventAccumulator(gen)
      gen.AddScalar("s1", wall_time=1, step=100, value=20)
      ev1 = event_pb2.Event(
          wall_time=2, step=0, file_version="brain.Event:1"
      )
      graph_bytes = tf.compat.v1.GraphDef().SerializeToString()
      ev2 = event_pb2.Event(wall_time=3, step=0, graph_def=graph_bytes)
      gen.AddEvent(ev1)
      gen.AddEvent(ev2)
      acc.Reload()
      self.assertEqual([x.step for x in acc.Scalars("s1")], [100])
  
imports: import os
  import numpy
  import tensorflow
  from tensorboard.backend.event_processing import event_accumulator
  from tensorboard.compat.proto import config_pb2
  from tensorboard.compat.proto import event_pb2
  from tensorboard.compat.proto import graph_pb2
  from tensorboard.compat.proto import meta_graph_pb2
  from tensorboard.compat.proto import summary_pb2
  from tensorboard.plugins.distribution import compressor
  from tensorboard.util import tensor_util
  from tensorboard.util import test_util
  from tensorboard.util import tb_logging
label_desc: Use image node_id 16 for calling the MockingEventAccumulatorTest obj's underlying member method code with example usage: obj.testOnlySummaryEventsTriggerDiscards() without return types