@Test
 public void addGraph_overlap() {
   DirectedGraph<Integer, String> graph = Graphs.createDirected(directedGraph.config());
   populateInputGraph(graph);
   // Add an edge that is in 'graph' (overlap)
   builder.addEdge(E12, N1, N2);
   builder.addGraph(graph);
   assertThat(builder.build()).isEqualTo(graph);
 }
 @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 addGraph_inconsistentEdges() {
   DirectedGraph<Integer, String> graph = Graphs.createDirected(directedGraph.config());
   populateInputGraph(graph);
   builder.addEdge(E21, N3, N1);
   try {
     builder.addGraph(graph);
     fail(
         "Should have rejected a graph whose edge definitions were inconsistent with existing"
             + "builder state");
   } catch (IllegalArgumentException expected) {
   }
 }
 @Test
 public void addGraph() {
   DirectedGraph<Integer, String> graph = Graphs.createDirected(directedGraph.config());
   populateInputGraph(graph);
   assertThat(builder.addGraph(graph).build()).isEqualTo(graph);
 }