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: pickfirst.rs
    path of file: ./repos/serde_with/serde_with/tests/serde_as
    
    the code of the file until where you have to start completion: use super::*;
use serde_with::{formats::SpaceSeparator, PickFirst};

#[test]
fn test_pick_first_two() {
    #[serde_as]
    #[derive(Debug, Serialize, Deserialize, PartialEq)]
    struct S(#[serde_as(as = "PickFirst<(_, DisplayFromStr)>")] u32);

    is_equal(S(123), expect![[r#"123"#]]);
    check_deserialization(S(123), r#""123""#);
  
    
fn test_pick_first_two() {
    #[serde_as]
    #[derive(Debug, Serialize, Deserialize, PartialEq)]
    struct S(#[serde_as(as = "PickFirst<(_, DisplayFromStr)>")] u32);

    is_equal(S(123), expect![[r#"123"#]]);
    check_deserialization(S(123), r#""123""#);
    check_error_deserialization::<S>(
        r#""Abc""#,
        expect![[r#"
            PickFirst could not deserialize any variant:
              First: invalid type: string "Abc", expected u32
              Second: invalid digit found in string"#]],
    );

    #[serde_as]
    #[derive(Debug, Serialize, Deserialize, PartialEq)]
    struct S2(#[serde_as(as = "PickFirst<(DisplayFromStr, _)>")] u32);

    is_equal(S2(123), expect![[r#""123""#]]);
    check_deserialization(S2(123), r#"123"#);

    #[serde_as]
    #[derive(Debug, Serialize, Deserialize, PartialEq)]
    struct S3(
        #[serde_as(as = "PickFirst<(_, StringWithSeparator::<SpaceSeparator, String>,)>")]
        Vec<String>,
    );
    is_equal(
        S3(vec!["A".to_string(), "B".to_string(), "C".to_string()]),
        expect![[r#"
            [
              "A",
              "B",
              "C"
            ]"#]],
    );
    check_deserialization(
        S3(vec!["A".to_string(), "B".to_string(), "C".to_string()]),
        r#""A B C""#,
    );

    #[serde_as]
    #[derive(Debug, Serialize, Deserialize, PartialEq)]
    struct S4(
        #[serde_as(as = "PickFirst<(StringWithSeparator::<CommaSeparator, String>, _,)>")]
        Vec<String>,
    );
    is_equal(
        S4(vec!["A".to_string(), "B".to_string(), "C".to_string()]),
        expect![[r#""A,B,C""#]],
    );
    check_deserialization(
        S4(vec!["A".to_string(), "B".to_string(), "C".to_string()]),
        r#"["A", "B", "C"]"#,
    );
}