public void TestParsing02() {
var g = new Grammar(new List<Production>{
CFGParser.Production("<X_0> → <X_1>"),
CFGParser.Production("<X_1> → 'x1' 'x2'"),
CFGParser.Production("<X_1> → ε")
}, Nonterminal.Of("X_0"));
var sentences = new List<Sentence>();
sentences.Add(Sentence.FromWords("x1 x2"));
ExecuteTest(g, sentences);
}