@Test
public void testIsValidSum_IMolecularFormula() {

    IMolecularFormula formula = new MolecularFormula();
    formula.addIsotope(ifac.getMajorIsotope("C"), 1);
    formula.addIsotope(ifac.getMajorIsotope("H"), 100);
    List<IRule> rules = new ArrayList<IRule>();
    rules.add(new MMElementRule());
    MolecularFormulaChecker MFChecker = new MolecularFormulaChecker(rules);
    Assert.assertEquals(0.0, MFChecker.isValidSum(formula), 0.001);
}