You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: utils.rs
    path of file: ./repos/graphql-engine/v3/engine/src
    
    the code of the file until where you have to start completion: pub mod async_map;
pub mod json_ext;
use serde::{de::DeserializeOwned, ser::SerializeMap, Deserialize, Serialize};
use std::{collections::HashMa
    
    fn test_hashmap_with_serializable_key() {
        #[derive(Serialize, Deserialize, Hash, PartialEq, Eq, Debug, Clone)]
        struct Foo {
            x: u32,
        }

        let mut test_map: HashMap<Foo, String> = HashMap::new();
        test_map.insert(Foo { x: 1 }, "hello".to_string());

        // The `test_map` cannot be serialized as is because
        // the key by default is serialized to a JSON object
        // and the JSON spec mandates that in a JSON object, the
        // key must be a String.

        assert!(serde_json::to_string(&test_map).is_err());

        let test_map_with_serializable_key = HashMapWithJsonKey(test_map.clone());

        let serialized_test_map_with_serializable_key =
            serde_json::to_string(&test_map_with_serializable_key).unwrap();

        assert_eq!(
            serialized_test_map_with_serializable_key,
            "{\"{\\\"x\\\":1}\":\"hello\"}"
        );

        let deserialized_test_map_with_serializable_key: HashMapWithJsonKey<Foo, String> =
            serde_json::from_str(&serialized_test_map_with_serializable_key).unwrap();

        assert_eq!(test_map, deserialized_test_map_with_serializable_key.0);
    }