code: def s3_join(*args):
      """Joins an S3 directory path as a replacement for os.path.join."""
      return "/".join(args)
  
file_path: tensorboard/tensorboard/summary/writer/event_file_writer_s3_test.py
imports: import boto3
  import os
  import unittest
  from tensorboard.summary.writer.event_file_writer import EventFileWriter
  from tensorboard.compat import tf
  from tensorboard.compat.proto import event_pb2
  from tensorboard.compat.proto.summary_pb2 import Summary
  from tensorboard.compat.tensorflow_stub.io import gfile
  from tensorboard.compat.tensorflow_stub.pywrap_tensorflow import PyRecordReader_New
  from moto import mock_s3
  from tensorboard import test
label_desc: Use image node_id 2 for calling a global function with example usage: s3_join() and returns: str