public void ParseVariable()
{
Parser parser = new Parser("X.");
IExpression expression = parser.ParseExpression();
Assert.IsNotNull(expression);
Assert.IsInstanceOfType(expression, typeof(VariableExpression));
VariableExpression varexpression = (VariableExpression)expression;
Assert.AreEqual("X", varexpression.Variable.Name);
Assert.IsNull(parser.ParseExpression());
}