### Question:
GuavaTrackingModuleGraph implements ModuleGraph<TrackingModuleDependency> { @Override public void addModule(HWModule vertex) { graph.addNode(vertex); } GuavaTrackingModuleGraph(MutableNetwork<HWModule, TrackingModuleDependency> graph); @Override Optional<TrackingModuleDependency> findDependency(HWModule vertex1, HWModule vertex2); @Override void addDependency(TrackingModuleDependency dependency); @Override void addModule(HWModule vertex); @Override Collection<HWModule> modules(); @Override Collection<HWModule> dependencies(HWModule vertex);  }### Answer:
@Test void addModuleShouldAddVertexToJungGraph() { testee.addModule(m1); assertThat(graph.nodes()).contains(m1); }
@Test void addModuleShouldFailIfVertexAlreadyAdded() { testee.addModule(m1); testee.addModule(m1); assertThat(graph.nodes().size()).isEqualTo(1); }