graph.setEntry(v1);
        v2 = graph.addVertex(new ArtifactMetadata("g", "a2", "1.0"));
        v3 = graph.addVertex(new ArtifactMetadata("g", "a3", "1.0"));
        v4 = graph.addVertex(new ArtifactMetadata("g", "a4", "1.0"));

        // v1-->v2
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.2", true, null, null, 2, 2));

        assertEquals(c2, c1, "expected " + v2 + ".equals( " + v1 + " )");
    }

    private void checkVersionsHaveSameOrder(String v1, String v2) {
        ComparableVersion c1 = new ComparableVersion(v1);
        ComparableVersion c2 = new ComparableVersion(v2);
        assertEquals(0, c1.compareTo(c2), "expected " + v1 + " == " + v2);
        assertEquals(0, c2.compareTo(c1), "expected " + v2 + " == " + v1);
    }

        graph.setEntry(v1);
        v2 = graph.addVertex(new ArtifactMetadata("g", "a2", "1.0"));
        v3 = graph.addVertex(new ArtifactMetadata("g", "a3", "1.0"));
        v4 = graph.addVertex(new ArtifactMetadata("g", "a4", "1.0"));

        // v1-->v2
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.1", true, null, null, 2, 1));
        graph.addEdge(v1, v2, new MetadataGraphEdge("1.2", true, null, null, 2, 2));

    }

    static void addEdge(Graph graph, String v1, String v2) throws CycleDetectedException {
        Vertex vx1 = graph.addVertex(v1);
        Vertex vx2 = graph.addVertex(v2);
        graph.addEdge(vx1, vx2);
    }

    static boolean hasEdge(Graph graph, String v1, String v2) {
        Vertex vx1 = graph.getVertex(v1);
        Vertex vx2 = graph.getVertex(v2);

            ArtifactVersion v1 = new DefaultArtifactVersion(e1.getVersion());
            ArtifactVersion v2 = new DefaultArtifactVersion(e2.getVersion());

            if (newerFirst) {
                return v1.compareTo(v2) > 0 ? e1 : e2;
            }

            return v1.compareTo(v2) > 0 ? e2 : e1;
        }

        if (closerFirst) {
            return depth1 < depth2 ? e1 : e2;
        }

    }

    @Test
    void testHashCode() {
        ArtifactVersion v1 = newArtifactVersion("1");
        ArtifactVersion v2 = newArtifactVersion("1.0");
        assertTrue(v1.equals(v2));
        assertEquals(v1.hashCode(), v2.hashCode());
    }

    @Test
    void testEqualsNullSafe() {
        assertFalse(newArtifactVersion("1").equals(null));
    }

    @Test