@Test
public void testOrder() {

    VisitedAtoms visitedAtoms = new VisitedAtoms();
    ILigand ligand1 = new Ligand(molecule, visitedAtoms, molecule.getAtom(1), molecule.getAtom(4));
    ILigand ligand2 = new Ligand(molecule, visitedAtoms, molecule.getAtom(1), molecule.getAtom(3));
    ILigand ligand3 = new Ligand(molecule, visitedAtoms, molecule.getAtom(1), molecule.getAtom(2));
    ILigand ligand4 = new Ligand(molecule, visitedAtoms, molecule.getAtom(1), molecule.getAtom(0));
    List<ILigand> ligands = new ArrayList<ILigand>();
    ligands.add(ligand1);
    ligands.add(ligand2);
    ligands.add(ligand3);
    ligands.add(ligand4);
    Collections.sort(ligands, new MassNumberRule());
    Assert.assertNotNull(ligands.get(0));
    Assert.assertEquals("H", ligands.get(0).getLigandAtom().getSymbol());
    Assert.assertEquals("H", ligands.get(1).getLigandAtom().getSymbol());
    Assert.assertEquals(2, ligands.get(1).getLigandAtom().getMassNumber().intValue());
    Assert.assertEquals("C", ligands.get(2).getLigandAtom().getSymbol());
    Assert.assertEquals("C", ligands.get(3).getLigandAtom().getSymbol());
    Assert.assertEquals(13, ligands.get(3).getLigandAtom().getMassNumber().intValue());
}