rust/library/std/src/error/tests.rs

use super::Error;
use crate::fmt;

#[derive(Debug, PartialEq)]
struct A;
#[derive(Debug, PartialEq)]
struct B;

impl fmt::Display for A {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "A")
    }
}
impl fmt::Display for B {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "B")
    }
}

impl Error for A {}
impl Error for B {}

#[test]
fn downcasting() {
    let mut a = A;
    let a = &mut a as &mut (dyn Error + 'static);
    assert_eq!(a.downcast_ref::<A>(), Some(&A));
    assert_eq!(a.downcast_ref::<B>(), None);
    assert_eq!(a.downcast_mut::<A>(), Some(&mut A));
    assert_eq!(a.downcast_mut::<B>(), None);

    let a: Box<dyn Error> = Box::new(A);
    match a.downcast::<B>() {
        Ok(..) => panic!("expected error"),
        Err(e) => assert_eq!(*e.downcast::<A>().unwrap(), A),
    }
}

use crate::backtrace;
use crate::env;
use crate::error::Report;

#[derive(Debug)]
struct SuperError {
    side: SuperErrorSideKick,
}

impl fmt::Display for SuperError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "SuperError is here!")
    }
}

impl Error for SuperError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        Some(&self.side)
    }
}

#[derive(Debug)]
struct SuperErrorSideKick;

impl fmt::Display for SuperErrorSideKick {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "SuperErrorSideKick is here!")
    }
}

impl Error for SuperErrorSideKick {}

#[test]
fn single_line_formatting() {
    let error = SuperError { side: SuperErrorSideKick };
    let report = Report::new(&error);
    let actual = report.to_string();
    let expected = String::from("SuperError is here!: SuperErrorSideKick is here!");

    assert_eq!(expected, actual);
}

#[test]
fn multi_line_formatting() {
    let error = SuperError { side: SuperErrorSideKick };
    let report = Report::new(&error).pretty(true);
    let actual = report.to_string();
    let expected =
        String::from("SuperError is here!\n\nCaused by:\n    SuperErrorSideKick is here!");

    assert_eq!(expected, actual);
}

#[test]
fn error_with_no_sources_formats_single_line_correctly() {
    let report = Report::new(SuperErrorSideKick);
    let actual = report.to_string();
    let expected = String::from("SuperErrorSideKick is here!");

    assert_eq!(expected, actual);
}

#[test]
fn error_with_no_sources_formats_multi_line_correctly() {
    let report = Report::new(SuperErrorSideKick).pretty(true);
    let actual = report.to_string();
    let expected = String::from("SuperErrorSideKick is here!");

    assert_eq!(expected, actual);
}

#[test]
fn error_with_backtrace_outputs_correctly() {
    use backtrace::Backtrace;

    env::remove_var("RUST_BACKTRACE");

    #[derive(Debug)]
    struct ErrorWithBacktrace<'a> {
        msg: &'a str,
        trace: Backtrace,
    }

    impl<'a> fmt::Display for ErrorWithBacktrace<'a> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "Error with backtrace: {}", self.msg)
        }
    }

    impl<'a> Error for ErrorWithBacktrace<'a> {
        fn backtrace(&self) -> Option<&Backtrace> {
            Some(&self.trace)
        }
    }

    let msg = String::from("The source of the error");
    let report = Report::new(ErrorWithBacktrace { msg: &msg, trace: Backtrace::capture() })
        .pretty(true)
        .show_backtrace(true);

    let expected = String::from(
        "Error with backtrace: The source of the error\n\nStack backtrace:\ndisabled backtrace",
    );

    assert_eq!(expected, report.to_string());
}

#[derive(Debug)]
struct GenericError<D> {
    message: D,
    source: Option<Box<dyn Error + 'static>>,
}

impl<D> GenericError<D> {
    fn new(message: D) -> GenericError<D> {
        Self { message, source: None }
    }

    fn new_with_source<E>(message: D, source: E) -> GenericError<D>
    where
        E: Error + 'static,
    {
        let source: Box<dyn Error + 'static> = Box::new(source);
        let source = Some(source);
        GenericError { message, source }
    }
}

impl<D> fmt::Display for GenericError<D>
where
    D: fmt::Display,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt::Display::fmt(&self.message, f)
    }
}

impl<D> Error for GenericError<D>
where
    D: fmt::Debug + fmt::Display,
{
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        self.source.as_deref()
    }
}

#[test]
fn error_formats_single_line_with_rude_display_impl() {
    #[derive(Debug)]
    struct MyMessage;

    impl fmt::Display for MyMessage {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.write_str("line 1\nline 2")?;
            f.write_str("\nline 3\nline 4\n")?;
            f.write_str("line 5\nline 6")?;
            Ok(())
        }
    }

    let error = GenericError::new(MyMessage);
    let error = GenericError::new_with_source(MyMessage, error);
    let error = GenericError::new_with_source(MyMessage, error);
    let error = GenericError::new_with_source(MyMessage, error);
    let report = Report::new(error);
    let expected = r#"line 1
line 2
line 3
line 4
line 5
line 6: line 1
line 2
line 3
line 4
line 5
line 6: line 1
line 2
line 3
line 4
line 5
line 6: line 1
line 2
line 3
line 4
line 5
line 6"#;

    let actual = report.to_string();
    assert_eq!(expected, actual);
}

#[test]
fn error_formats_multi_line_with_rude_display_impl() {
    #[derive(Debug)]
    struct MyMessage;

    impl fmt::Display for MyMessage {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.write_str("line 1\nline 2")?;
            f.write_str("\nline 3\nline 4\n")?;
            f.write_str("line 5\nline 6")?;
            Ok(())
        }
    }

    let error = GenericError::new(MyMessage);
    let error = GenericError::new_with_source(MyMessage, error);
    let error = GenericError::new_with_source(MyMessage, error);
    let error = GenericError::new_with_source(MyMessage, error);
    let report = Report::new(error).pretty(true);
    let expected = r#"line 1
line 2
line 3
line 4
line 5
line 6

Caused by:
   0: line 1
      line 2
      line 3
      line 4
      line 5
      line 6
   1: line 1
      line 2
      line 3
      line 4
      line 5
      line 6
   2: line 1
      line 2
      line 3
      line 4
      line 5
      line 6"#;

    let actual = report.to_string();
    assert_eq!(expected, actual);
}

#[test]
fn errors_that_start_with_newline_formats_correctly() {
    #[derive(Debug)]
    struct MyMessage;

    impl fmt::Display for MyMessage {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.write_str("\nThe message\n")
        }
    }

    let error = GenericError::new(MyMessage);
    let error = GenericError::new_with_source(MyMessage, error);
    let error = GenericError::new_with_source(MyMessage, error);
    let report = Report::new(error).pretty(true);
    let expected = r#"
The message


Caused by:
   0: The message
   1: The message"#;

    let actual = report.to_string();
    assert_eq!(expected, actual);
}

#[test]
fn errors_with_string_interpolation_formats_correctly() {
    #[derive(Debug)]
    struct MyMessage(usize);

    impl fmt::Display for MyMessage {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "Got an error code: ({}). ", self.0)?;
            write!(f, "What would you like to do in response?")
        }
    }

    let error = GenericError::new(MyMessage(10));
    let error = GenericError::new_with_source(MyMessage(20), error);
    let report = Report::new(error).pretty(true);
    let expected = r#"Got an error code: (20). What would you like to do in response?

Caused by:
    Got an error code: (10). What would you like to do in response?"#;
    let actual = report.to_string();
    assert_eq!(expected, actual);
}