code: def test_dask_mg_bfs_invalid_start(dask_client, directed):
      source_vertex = 10
      input_data_path = (
          RAPIDS_DATASET_ROOT_DIR_PATH / "netscience.csv"
      ).as_posix()
  
      print(f"dataset={input_data_path}")
      chunksize = dcg.get_chunksize(input_data_path)
  
      el = dask_cudf.read_csv(
          input_data_path,
          chunksize=chunksize,
          delimiter=" ",
          names=["src", "dst", "value"],
          dtype=["int32", "int32", "float32"],
      )
      newval = max(el.src.max().compute(), el.dst.max().compute()) + 1
      el.src = el.src.replace(source_vertex, newval)
      el.dst = el.dst.replace(source_vertex, newval)
  
      G = cugraph.Graph(directed=directed)
      G.from_dask_cudf_edgelist(el, "src", "dst")
  
      with pytest.raises(ValueError):
          dcg.bfs(G, source_vertex).compute()
  
      # invalid dtype (the default cudf.Series() dtype is int64)
      source_vertex = cudf.Series([0, 1])
      warning_msg = (
          "The 'start' values dtype must match "
          "the graph's vertices dtype."
      )
      with pytest.warns(UserWarning, match=warning_msg):
          dcg.bfs(G, source_vertex).compute()
  
file_path: cugraph/python/cugraph/cugraph/tests/traversal/test_bfs_mg.py
imports: import gc
  import random
  import pytest
  import cudf
  import cugraph
  import dask_cudf
  import cugraph.dask
  from cugraph.testing.utils import RAPIDS_DATASET_ROOT_DIR_PATH
label_desc: Use image node_id 3 for calling a global function with example usage: test_dask_mg_bfs_invalid_start(dask_client, directed) without return types