@Test
public void testGetTotalNaturalAbundance_IMolecularFormula() throws Exception {

    IMolecularFormula formula = new MolecularFormula();
    IIsotope carb = builder.newInstance(IIsotope.class, "C");
    carb.setNaturalAbundance(98.93);
    IIsotope cl = builder.newInstance(IIsotope.class, "Cl");
    cl.setNaturalAbundance(75.78);
    formula.addIsotope(carb);
    formula.addIsotope(cl);
    double totalAbudance = MolecularFormulaManipulator.getTotalNaturalAbundance(formula);
    Assert.assertEquals(0.74969154, totalAbudance, 0.000001);
}