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: non_identifier_identifier.rs
    path of file: ./repos/ron/tests
    
    the code of the file until where you have to start completion: macro_rules! test_non_identifier {
    ($test_name:ident => $deserialize_method:ident($($deserialize_param:expr),*)) => {
        #[test]
  
    
        fn $test_name() {
            use serde::{Deserialize, Deserializer, de::Visitor, de::MapAccess};

            struct FieldVisitor;

            impl<'de> Visitor<'de> for FieldVisitor {
                type Value = FieldName;

                // GRCOV_EXCL_START
                fn expecting(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
                    fmt.write_str("an error")
                }
                // GRCOV_EXCL_STOP
            }

            struct FieldName;

            impl<'de> Deserialize<'de> for FieldName {
                fn deserialize<D: Deserializer<'de>>(deserializer: D)
                    -> Result<Self, D::Error>
                {
                    deserializer.$deserialize_method($($deserialize_param,)* FieldVisitor)
                }
            }

            struct StructVisitor;

            impl<'de> Visitor<'de> for StructVisitor {
                type Value = Struct;

                // GRCOV_EXCL_START
                fn expecting(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
                    fmt.write_str("a struct")
                }
                // GRCOV_EXCL_STOP

                fn visit_map<A: MapAccess<'de>>(self, mut map: A)
                    -> Result<Self::Value, A::Error>
                {
                    map.next_key::<FieldName>().map(|_| Struct)
                }
            }

            #[derive(Debug)]
            struct Struct;

            impl<'de> Deserialize<'de> for Struct {
                fn deserialize<D: Deserializer<'de>>(deserializer: D)
                    -> Result<Self, D::Error>
                {
                    deserializer.deserialize_struct("Struct", &[], StructVisitor)
                }
            }

            assert_eq!(
                ron::from_str::<Struct>("(true: 4)").unwrap_err().code,
                ron::Error::ExpectedIdentifier
            )
        }