code: def test_get_graphviz_source(self, sprinkler_graph):
      gv_src = """digraph G {
    graph [ dpi = 300 bgcolor="transparent" rankdir="LR"];
    Cloudy [ shape="ellipse" color="blue"];
    Rain [ shape="ellipse" color="blue"];
    Sprinkler [ shape="ellipse" color="blue"];
    WetGrass [ shape="ellipse" color="blue"];
    Cloudy -> Rain;
    Cloudy -> Sprinkler;
    Rain -> WetGrass;
    Sprinkler -> WetGrass;
  }
  """
      assert sprinkler_graph.get_graphviz_source() == gv_src
  
imports: from __future__ import division
  import copy
  from collections import Counter
  import pytest
  from causalnex.ebaybbn import BBNNode, JoinTree, JoinTreeCliqueNode, SepSet, build_bbn, build_bbn_from_conditionals, build_join_tree, combinations, make_moralized_copy, make_node_func, make_undirected_copy, priority_func, triangulate
  from causalnex.ebaybbn.exceptions import VariableNotInGraphError, VariableValueNotInDomainError
  from causalnex.ebaybbn.graph import Node, UndirectedNode
  from causalnex.ebaybbn.utils import get_args, get_original_factors, make_key
label_desc: Use image node_id 1 for calling the TestBBN obj's underlying member method code with example usage: obj.test_get_graphviz_source(sprinkler_graph) without return types