@Test
public void testReferenceRelation() {

    ClassNode c1 = new ClassNode("c1");
    ClassNode c2 = new ClassNode("c2");
    ReferencesRelation r1 = new ReferencesRelation(c1, c2, "READ_WRITE");
    assertThat(r1.toString()).isEqualTo("(c1)-[READ_WRITE]->(c2)");
    ReferencesRelation r2 = new ReferencesRelation();
    assertThat(r2.toString()).isEqualTo("(<NONE>)-[null]->(<NONE>)");
}