@Test
public void testGetNaturalExactMass_IMolecularFormula() throws Exception {

    IMolecularFormula formula = new MolecularFormula();
    formula.addIsotope(builder.newInstance(IIsotope.class, "C"));
    formula.addIsotope(builder.newInstance(IIsotope.class, "Cl"));
    double expectedMass = 0.0;
    expectedMass += Isotopes.getInstance().getNaturalMass(builder.newInstance(IElement.class, "C"));
    expectedMass += Isotopes.getInstance().getNaturalMass(builder.newInstance(IElement.class, "Cl"));
    double totalExactMass = MolecularFormulaManipulator.getNaturalExactMass(formula);
    Assert.assertEquals(expectedMass, totalExactMass, 0.000001);
}