public void ParseNegativeInteger()
{
Lexer lexer = new Lexer("-42");
var token = lexer.NextToken();
Assert.IsNotNull(token);
Assert.AreEqual(TokenType.Operator, token.TokenType);
Assert.AreEqual("-", token.Value);
token = lexer.NextToken();
Assert.IsNotNull(token);
Assert.AreEqual("42", token.Value);
Assert.AreEqual(TokenType.Integer, token.TokenType);
Assert.IsNull(lexer.NextToken());
}