@Test public void benzimidazole() throws Exception {

    Graph g = Graph.fromSmiles("c1nc2ccccc2[nH]1");
    Matching m = Matching.empty(g);
    MaximumMatching.maximise(g,
                             m,
                             0,
                             IntSet.noneOf(8)); // not the 'nH'
    assertThat(m.matches(), hasItems(Tuple.of(0, 1),
                                     Tuple.of(2, 3),
                                     Tuple.of(4, 5),
                                     Tuple.of(6, 7)));
}