public void ParseReturn()
{
ModelParser parser = new ModelParser("^10");
IExpression expression = parser.ParseExpression();
Assert.IsNotNull(expression);
Assert.IsInstanceOfType(expression, typeof(ReturnExpression));
ReturnExpression rexpression = (ReturnExpression)expression;
Assert.IsInstanceOfType(rexpression.Expression, typeof(ConstantExpression));
Assert.AreEqual(10, ((ConstantExpression)rexpression.Expression).Value);
}