@Test
public void edge() {

    Graph g = new Graph(5);
    g.addAtom(mock(Atom.class));
    g.addAtom(mock(Atom.class));
    g.addAtom(mock(Atom.class));
    g.addEdge(new Edge(0, 1, Bond.IMPLICIT));
    g.addEdge(new Edge(1, 2, Bond.IMPLICIT));
    assertThat(g.edge(0, 1), is(new Edge(0, 1, Bond.IMPLICIT)));
    assertThat(g.edge(1, 2), is(new Edge(1, 2, Bond.IMPLICIT)));
}