code: def testGetOnlyDirInDir(self):
      self.createFiles({"dir1": {"dir2": {"file.txt": "testing"}}})
      self.assertEqual(
          self.relpath("dir1", "dir2"),
          io_utils.get_only_uri_in_dir(self.relpath("dir1")),
      )
  
imports: import os
  from unittest import mock
  import tensorflow
  from tfx.dsl.io import fileio
  from tfx.utils import io_utils
  from tensorflow.python.lib.io import file_io
label_desc: Use image node_id 15 for calling the IoUtilsTest obj's underlying member method code with example usage: obj.testGetOnlyDirInDir() without return types