public void EvaluateCanSubstitueConstants()
 {
     Parse parse = new Parse("q= 7");
     Evaluate eval = new Evaluate(parse);
     eval.Execute();
     Parse parseTwo = new Parse("q + 5");
     eval.ParsedInput = parseTwo;
     eval.SubstituteConstants();
     Assert.AreEqual(7, eval.ParsedInput.FirstNumArg);
 }