code: @Test public void nested() throws ScanException {
    Tokenizer tokenizer=new Tokenizer("a${b${c}}d");
    Parser parser=new Parser(tokenizer.tokenize());
    Node node=parser.parse();
    Node witness=new Node(Node.Type.LITERAL,"a");
    Node bLiteralNode=new Node(Node.Type.LITERAL,"b");
    Node cLiteralNode=new Node(Node.Type.LITERAL,"c");
    Node bVariableNode=new Node(Node.Type.VARIABLE,bLiteralNode);
    Node cVariableNode=new Node(Node.Type.VARIABLE,cLiteralNode);
    bLiteralNode.next=cVariableNode;
    witness.next=bVariableNode;
    witness.next.next=new Node(Node.Type.LITERAL,"d");
    assertEquals(witness,node);
  }
  