Graph graph2 = new Graph();
        addEdge(graph2, "a", "b");
        addEdge(graph2, "b", "c");
        CycleDetectedException cde = assertThrows(CycleDetectedException.class, () -> addEdge(graph2, "c", "a"));
        List<String> cycle = cde.getCycle();
        assertNotNull(cycle, "Cycle should be not null");
        assertTrue(cycle.contains("a"), "Cycle contains 'a'");