code: def test_descendants_at_distance_missing_source(self):
      with pytest.raises(nx.NetworkXError):
          nx.descendants_at_distance(self.G, "abc", 0)
  
imports: from functools import partial
  import pytest
  import networkx
label_desc: Use image node_id 12 for calling the TestBFS obj's underlying member method code with example usage: obj.test_descendants_at_distance_missing_source() without return types