Rustlings advanced_errs2测试是否不够严谨

[QIUZHILEI]

#[test]
fn test_empty() {
let res = "".parse::();
assert_eq!(res, Err(ParseClimateError::Empty));
assert_eq!(res.unwrap_err().to_string(), "empty input");
}

#[test]
fn test_short() {
let res = "Boston,1991".parse::();
assert_eq!(res, Err(ParseClimateError::BadLen));
assert_eq!(res.unwrap_err().to_string(), "incorrect number of fields");
}
应该在加一个测试，测试的res为 "Boston"，原因如下：

如果写的模式匹配是这样的:

fn from_str(s: &str) -> Result<Self, Self::Err> {
let v: Vec<_> = s.split(',').collect();
let (city, year, temp) = match &v[..] {
[some_str] => return Err(ParseClimateError::Empty), //some_str 可能是"" 或 "Boston"
……
};
……
}
考虑以上匹配，如果按照原来的测试，给定的字符串是""，应该返回Empty 错误，但是如果给定的字符串是"Boston"，那么也会匹配成功，但是应该返回的是BadLen错误

[yfblock]

我采取了不一样的处理方法，将字符串长度进行了单独处理，因此我觉得目前的测试案例已经比较完善，Empty的处理优先级应该是最高。因此在最开始进行处理会更好？

fn from_str(s: &str) -> Result<Self, Self::Err> {
    if s.len() == 0 {
        return Err(ParseClimateError::Empty);
    }
    let v: Vec<_> = s.split(',').collect();
    let (city, year, temp) = match &v[..] {
        ["", ..] => return Err(ParseClimateError::NoCity),
        [city, year, temp] => (city.to_string(), year, temp),
        _ => return Err(ParseClimateError::BadLen),
    };
    let year: u32 = year.parse()?;
    let temp: f32 = temp.parse()?;
    Ok(Climate { city, year, temp })
}

[QIUZHILEI]

//match这样写 也可以通过测试
     let (city, year, temp) = match &v[..] {
          [_] => return Err(ParseClimateError::Empty),
          ["",_,_]=> return Err(ParseClimateError::NoCity),
          [city, year, temp] =>(city.to_string(), year, temp),
          _ => return Err(ParseClimateError::BadLen),
      };
//如果你加一个这样的测试
    #[test]
    fn test_only_city(){
        let res = "Paris".parse::<Climate>();
        assert_eq!(res, Err(ParseClimateError::BadLen));
        assert_eq!(res.unwrap_err().to_string(), "incorrect number of fields");
    }

会测试失败

---- test::test_only_city stdout ----
thread 'test::test_only_city' panicked at 'assertion failed: `(left == right)`
  left: `Err(Empty)`,
 right: `Err(BadLen)`', src\main.rs:153:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

//我的match这样写的 ，加了那个测试也会成功 ，你的那个也会成功

    let (city, year, temp) = match &v[..] {
          [""] => return Err(ParseClimateError::Empty),
          ["",_,_]=> return Err(ParseClimateError::NoCity),
          [city, year, temp] =>(city.to_string(), year, temp),
          _ => return Err(ParseClimateError::BadLen),
      };

//所以第一个的match那样写应该有问题，但是不加那个测试就不会出问题
PS：这也是今天下午群里的人提出来的问题，我测试了一下，果真如此

[QIUZHILEI]

//这是写的那个 from_str
fn from_str(s: &str) -> Result<Self, Self::Err> {
        let v: Vec<_> = s.split(',').collect();
        let (city, year, temp) = match &v[..] {
            [""] => return Err(ParseClimateError::Empty),
            ["",_,_]=> return Err(ParseClimateError::NoCity),
            [city, year, temp] =>(city.to_string(), year, temp),
            _ => return Err(ParseClimateError::BadLen),
        };
        let year: u32 = year.parse()?;
        let temp: f32 = temp.parse()?;
        Ok(Climate { city, year, temp })
    }