class_docstr: For the "compare" command.
class_docstr_tok: ["For","the","``","compare","''","command","."]
code: def test_placeholder_error(self):
      parser = cmd_line_parser.CmdLineParser()
      with self.assertRaisesRegex(
          argument_parser.ParserError,
          (
              'argument --inputs/-i: Error with value "_NOT_WORD_INPUT_VAR", got'
              ' ValueError: Placeholder "word" not found in input'
          ),
      ):
          parser.parse_line(
              "compare _test_lhs_fn _test_rhs_fn --inputs _NOT_WORD_INPUT_VAR"
          )
  
imports: from __future__ import annotations
  import sys
  from unittest import mock
  from absl.testing import absltest
  from google.generativeai.notebook import argument_parser
  from google.generativeai.notebook import cmd_line_parser
  from google.generativeai.notebook import model_registry
  from google.generativeai.notebook import parsed_args_lib
  from google.generativeai.notebook import post_process_utils
  from google.generativeai.notebook.lib import llm_function
  from google.generativeai.notebook.lib import llmfn_output_row
  from google.generativeai.notebook.lib import llmfn_outputs
  from google.generativeai.notebook.lib import model
label_desc: Use image node_id 3 for calling the CmdLineParserCompareTest obj's underlying member method code with example usage: obj.test_placeholder_error() without return types