{"ast_node_type":"variable","tokens":[{"end":50,"kind":"keyword","start":0,"text":"let"}]}
    let (t, r) = parse_codeblock(buf1.as_bytes());
    let buf1 = "```rust\ncode\ncode\n```\nleftovers";
    assert_eq!(t, MdTree::CodeBlock { txt: "code\ncode", lang: Some("rust") });