{"ast_node_type":"other","tokens":[{"end":86,"kind":"keyword","start":0,"text":"//"}]}
        // `None` is translated to empty string, meaning that there is nothing to fix.
    fn check<F: Fn(&str) -> Option<String>>(fun: F, input: &str, expect: Expect) {
        let output = fun(input).unwrap_or_default();