public void MonomialsAddResultsInException2()
        {
            IExpressionParser parser        = new ExpressionParser();
            Monomial          monomial      = new Monomial(1, "x", 2, parser);
            Monomial          monomialToAdd = new Monomial(2, "x", 3, parser);

            Assert.Throws <InvalidMonomialOperationException>(() =>
                                                              monomial.AddMonomialWithSameVariable(monomialToAdd));
        }
        public void MonomialsAddResultsIn3()
        {
            IExpressionParser parser        = new ExpressionParser();
            Monomial          monomial      = new Monomial(1, "", null, parser);
            Monomial          monomialToAdd = new Monomial(2, "", null, parser);
            Monomial          result        = monomial.AddMonomialWithSameVariable(monomialToAdd);

            Assert.AreEqual("3", result.Expression);
        }