ArtifactSpec a = createArtifactSpec("a", "1.0");
        ArtifactSpec b = a.addDependency("b", "1.0");
        ArtifactSpec c2 = b.addDependency("c", "2.0");
        c2.addDependency("d", "1.0");

        ArtifactSpec e = createArtifactSpec("e", "1.0");
        ArtifactSpec c1 = e.addDependency("c", "1.0");
        ArtifactSpec f = c1.addDependency("f", "1.0");