@Test public void relativeBond() throws Exception {

    assertThat(new Edge(2, 3, Bond.SINGLE).bond(2), is(Bond.SINGLE));
    assertThat(new Edge(2, 3, Bond.SINGLE).bond(3), is(Bond.SINGLE));
    assertThat(new Edge(2, 3, Bond.UP).bond(2), is(Bond.UP));
    assertThat(new Edge(2, 3, Bond.UP).bond(3), is(Bond.DOWN));
    assertThat(new Edge(2, 3, Bond.DOWN).bond(2), is(Bond.DOWN));
    assertThat(new Edge(2, 3, Bond.DOWN).bond(3), is(Bond.UP));
}