@Test
public void testImplicitHydrogen() {

    ILigand ligand1 = new ImplicitHydrogenLigand(molecule, new VisitedAtoms(), molecule.getAtom(1));
    ILigand ligand2 = new Ligand(molecule, new VisitedAtoms(), molecule.getAtom(1), molecule.getAtom(3));
    ISequenceSubRule<ILigand> rule = new MassNumberRule();
    Assert.assertEquals(-1, rule.compare(ligand1, ligand2));
    Assert.assertEquals(1, rule.compare(ligand2, ligand1));
}