code: def testGetOnlyFileInDir(self):
      self.createFiles({"dir": {"file.txt": "testing"}})
      self.assertEqual(
          self.relpath("dir", "file.txt"),
          io_utils.get_only_uri_in_dir(self.relpath("dir")),
      )
  
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 14 for calling the IoUtilsTest obj's underlying member method code with example usage: obj.testGetOnlyFileInDir() without return types