These test codes for call func make strange error

[rocket049]

These test codes for call func make strange error. Function 'tmpl_test1' can not pass, But function 'tmpl_test2' can pass.
The different between them:
In tmpl_test1, the function is stored in a map;
In tmpl_test2, the function is used straight.

#[cfg(test)]
mod tests {
    use std::collections::HashMap;
    use gtmpl::{gtmpl_fn, template, Value};
    use gtmpl_value::{self, FuncError, Function};

    gtmpl_fn!(
        fn shout(n: i64) -> Result<String, FuncError> {
            let mut v = Vec::new();
            for _ in 0..n {
                v.push("wang".to_string());
            }
            Ok(v.join(","))
        }
    );

    #[test]
    fn tmpl_test1() {
        let mut a: HashMap<String, Value> = HashMap::new();
        a.insert(
            "shout".to_string(),
            Value::Function(Function { f: shout }),
        );
        let equal = template(r#"{{ call .shout 3 }}"#, a);
        if equal.is_ok() {
            assert_eq!(&equal.unwrap(), "wang,wang,wang");
        } else {
            assert_eq!(&equal.unwrap_err().to_string(), "wang,wang,wang");
        }
    }
    #[test]
    fn tmpl_test2() {
        let equal: Result<String, gtmpl::TemplateError> = template(
            r#"{{ call . 3 }}"#,
            Value::Function(Function { f: shout }),
        );
        if equal.is_ok() {
            assert_eq!(&equal.unwrap(), "wang,wang,wang");
        } else {
            assert_eq!(&equal.unwrap_err().to_string(), "wang,wang,wang");
        }
    }
}