code: def testZero(self):
      self.assertEqual(upload_tracker.readable_bytes_string(0), "0 B")
  
imports: import sys
  from unittest import mock
  from tensorboard import test
  from tensorboard.uploader import upload_tracker
label_desc: Use image node_id 1 for calling the ReadableBytesStringTest obj's underlying member method code with example usage: obj.testZero() without return types