use crate::prelude::*; #[derive(Serialize, Document)] struct Ty { #[serde(serialize_with = "fun")] foo: String, } fn fun(_: &str, _: S) -> Result where S: serde::Serializer, { unimplemented!() } printer_test! { "output.json" => to_json(Ty), "output.toml" => to_toml(Ty), }