{"ast_node_type":"variable","tokens":[{"end":50,"kind":"keyword","start":0,"text":"let"}]}
    let (t, r) = parse_codeblock(buf2.as_bytes());
    let buf2 = "`````\ncode\ncode````\n`````\nleftovers";
    assert_eq!(t, MdTree::CodeBlock { txt: "code\ncode````", lang: None });