class_docstr: Test subclass of ReadlineUI that bypasses terminal manipulations.
code: def _display_output(self, screen_output):
      self.observers["screen_outputs"].append(screen_output)
  
imports: import os
  import argparse
  import tempfile
  from tensorflow.python.debug.cli import cli_config
  from tensorflow.python.debug.cli import debugger_cli_common
  from tensorflow.python.debug.cli import readline_ui
  from tensorflow.python.debug.cli import ui_factory
  from tensorflow.python.framework import test_util
  from tensorflow.python.lib.io import file_io
  from tensorflow.python.platform import gfile
  from tensorflow.python.platform import googletest
label_desc: Use image node_id 3 for calling the MockReadlineUI obj's underlying member method code with example usage: obj._display_output(screen_output) without return types