@Test
 public void addGraph_incompatibleMultigraphConfig() {
   try {
     DirectedGraph multigraph = Graphs.createDirected(Graphs.MULTIGRAPH);
     ImmutableDirectedGraph.Builder immutableGraphBuilder = ImmutableDirectedGraph.builder();
     immutableGraphBuilder.addGraph(multigraph);
     fail("Should have rejected a graph with an incompatible multigraph configuration");
   } catch (IllegalArgumentException expected) {
   }
 }
 @Test
 public void addGraph_incompatibleSelfLoopConfig() {
   try {
     DirectedGraph graph = Graphs.createDirected(Graphs.config().noSelfLoops());
     ImmutableDirectedGraph.Builder immutableGraphBuilder = ImmutableDirectedGraph.builder();
     immutableGraphBuilder.addGraph(graph);
     fail("Should have rejected a graph with an incompatible self-loop configuration");
   } catch (IllegalArgumentException expected) {
   }
 }
 @Test
 public void copyOf() {
   DirectedGraph<Integer, String> graph = Graphs.createDirected(directedGraph.config());
   populateInputGraph(graph);
   assertThat(ImmutableDirectedGraph.copyOf(graph)).isEqualTo(graph);
 }
 @Override
 public ImmutableDirectedGraph<Integer, String> createGraph() {
   builder = ImmutableDirectedGraph.builder(Graphs.config().noSelfLoops());
   return builder.build();
 }