ohno 0.3.5

High-quality Rust error handling.
Documentation 
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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

#![cfg_attr(coverage_nightly, coverage(off))] // coverage doesn't handle panics well

//! Test utilities for the ohno crate.
//!
//! This module is only available when the `test-util` feature is enabled.

/// Assert that an error message matches the expected value, accounting for potential backtraces.
///
/// This macro checks if the error's display representation exactly matches the expected string,
/// or if it starts with the expected string followed by a backtrace section.
///
/// # Examples
///
/// ```
/// # #[cfg(feature = "test-util")]
/// # {
/// use ohno::assert_error_message;
///
/// #[derive(ohno::Error)]
/// struct MyError {
///     inner: ohno::OhnoCore,
/// }
///
/// let error = MyError::caused_by("something went wrong");
/// assert_error_message!(error, "something went wrong");
/// # }
/// ```
#[macro_export]
macro_rules! assert_error_message {
    ($error:expr, $expected:expr) => {{
        let error_string = $error.to_string();
        let expected: &str = $expected;

        let test = move || {
            if error_string == expected {
                return ();
            }
            if let Some(remainder) = error_string.strip_prefix(expected) {
                // backtrace, caused by, or error trace indicators
                if remainder.starts_with("\n\nBacktrace:\n") || remainder.starts_with("\ncaused by: ") || remainder.starts_with("\n> ") {
                    return ();
                }
            }
            panic!("left : {expected}\nright: {error_string}");
        };
        test();
    }};
}

#[cfg(test)]
mod tests {
    use crate::OhnoCore;
    use crate::backtrace::Backtrace;

    #[derive(crate::Error)]
    struct MyTestError {
        inner: OhnoCore,
    }

    #[test]
    fn test_assert_error_message_exact_match() {
        let error = MyTestError::caused_by("test message");
        assert_error_message!(error, "test message");
    }

    #[test]
    fn test_assert_error_message_with_backtrace() {
        let mut error = MyTestError::caused_by("test message");
        // Force a backtrace (this will be empty in test mode without RUST_BACKTRACE)
        error.inner.data.backtrace = Backtrace::disabled();
        assert_error_message!(error, "test message");
    }

    #[test]
    #[should_panic(expected = "left : expected message\nright: actual message")]
    fn test_assert_error_message_mismatch() {
        let error = MyTestError::caused_by("actual message");
        assert_error_message!(error, "expected message");
    }
}