code: def test_convert_unknown_engine(tmp_path):
      pipe = Pipeline()
      pipe.add_component("comp1", Double())
      pipe.add_component("comp2", Double())
      pipe.connect("comp1", "comp2")
      pipe.connect("comp2", "comp1")
  
      with pytest.raises(
          ValueError, match="Unknown rendering engine 'unknown'"
      ):
          _convert(pipe.graph, engine="unknown")
  
file_path: haystack/test/core/pipeline/test_draw.py
imports: import os
  import filecmp
  from unittest.mock import patch, MagicMock
  import pytest
  import requests
  from haystack.core.pipeline import Pipeline
  from haystack.core.pipeline.draw.draw import _draw, _convert
  from haystack.core.errors import PipelineDrawingError
  from haystack.testing.sample_components import Double, AddFixedValue
label_desc: Use image node_id 5 for calling a global function with example usage: test_convert_unknown_engine(tmp_path) without return types