@Test
public void testGetString_Isotopes() {

    IMolecularFormula mf1 = new MolecularFormula();
    mf1.addIsotope(builder.newInstance(IIsotope.class, "C", 12), 9);
    mf1.addIsotope(builder.newInstance(IIsotope.class, "C", 13), 1);
    mf1.addIsotope(builder.newInstance(IIsotope.class, "H"), 16);
    Assert.assertEquals("C10H16", MolecularFormulaManipulator.getString(mf1));
}