code: def test_bfs_layers_missing_source(self):
      with pytest.raises(nx.NetworkXError):
          next(nx.bfs_layers(self.G, sources="abc"))
      with pytest.raises(nx.NetworkXError):
          next(nx.bfs_layers(self.G, sources=["abc"]))
  
imports: from functools import partial
  import pytest
  import networkx
label_desc: Use image node_id 10 for calling the TestBFS obj's underlying member method code with example usage: obj.test_bfs_layers_missing_source() without return types