public void AddNegativeIsotopeToFormula()
{
ChemicalFormula formulaA = new ChemicalFormula("C2H3NO");
ChemicalFormula formulaB = new ChemicalFormula("C2HNO");
Isotope h1 = PeriodicTable.GetElement("H")[1];
formulaA.Add(h1, -2);
Assert.AreEqual(formulaA, formulaB);
}