public void ParseTrue()
{
ModelParser parser = new ModelParser("true");
IExpression expression = parser.ParseExpression();
Assert.IsNotNull(expression);
Assert.IsInstanceOfType(expression, typeof(ConstantExpression));
ConstantExpression cexpression = (ConstantExpression)expression;
Assert.AreEqual(true, cexpression.Value);
Assert.AreEqual("true", expression.AsString());
}