### Question:
GuavaModuleGraph implements MetricModuleGraph<ModuleDependency> { @Override public void addModule(HWModule vertex) { graph.addNode(vertex); } GuavaModuleGraph(MutableNetwork<HWModule, ModuleDependency> graph); @Override Optional<ModuleDependency> findDependency(HWModule vertex1, HWModule vertex2); @Override void addDependency(final ModuleDependency dependency); @Override void addModule(HWModule vertex); @Override Collection<HWModule> modules(); @Override Collection<HWModule> dependencies(HWModule vertex); @Override Optional<Integer> fanInOf(HWModule module); @Override Optional<Integer> fanOutOf(HWModule module);  }### 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); }