test-that 0.1.0

// Copyright 2022 Google LLC
// Copyright 2026 Bradford Hovinen <bradford@hovinen.me>
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use crate::description::Description;
use crate::matcher::{Describable, Matcher, MatcherResult};
use std::fmt::{Debug, Display};

/// Matches the string representation of types that implement `Display`.
///
/// ```
/// # use test_that::prelude::*;
/// let result = "Hello, world!";
/// assert_that!(result, displays_as(eq("Hello, world!")));
/// ```
pub fn displays_as<InnerMatcher>(inner: InnerMatcher) -> __internal::DisplayMatcher<InnerMatcher> {
    __internal::DisplayMatcher { inner }
}

pub mod __internal {
    use super::*;

    #[doc(hidden)]
    pub struct DisplayMatcher<InnerMatcher> {
        pub(super) inner: InnerMatcher,
    }

    impl<T: Debug + Display + ?Sized, InnerMatcher: Matcher<String>> Matcher<T>
        for DisplayMatcher<InnerMatcher>
    {
        fn matches(&self, actual: &T) -> MatcherResult {
            self.inner.matches(&format!("{actual}"))
        }

        fn explain_match(&self, actual: &T) -> Description {
            format!(
                "which displays as a string {}",
                self.inner.explain_match(&format!("{actual}"))
            )
            .into()
        }
    }

    impl<InnerMatcher: Describable> Describable for DisplayMatcher<InnerMatcher> {
        fn describe(&self, matcher_result: MatcherResult) -> Description {
            match matcher_result {
                MatcherResult::Match => format!(
                    "displays as a string which {}",
                    self.inner.describe(MatcherResult::Match)
                )
                .into(),
                MatcherResult::NoMatch => format!(
                    "doesn't display as a string which {}",
                    self.inner.describe(MatcherResult::Match)
                )
                .into(),
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::displays_as;
    use crate::prelude::*;
    use indoc::indoc;
    use serial_test::serial;
    use std::fmt::{Debug, Display, Error, Formatter};

    #[test]
    fn display_matches_i32() -> TestResult<()> {
        let value = 32;
        verify_that!(value, displays_as(eq("32")))?;
        Ok(())
    }

    #[test]
    fn display_matches_str() -> TestResult<()> {
        let value = "32";
        verify_that!(value, displays_as(eq("32")))?;
        Ok(())
    }

    #[test]
    fn display_matches_struct() -> TestResult<()> {
        #[allow(dead_code)]
        #[derive(Debug)]
        struct Struct {
            a: i32,
            b: i64,
        }
        impl Display for Struct {
            fn fmt(&self, f: &mut Formatter<'_>) -> std::result::Result<(), Error> {
                write!(f, "{:?}", self)
            }
        }
        verify_that!(Struct { a: 123, b: 321 }, displays_as(eq("Struct { a: 123, b: 321 }")))?;
        Ok(())
    }

    #[test]
    #[serial]
    fn display_displays_error_message_with_explanation_from_inner_matcher() -> TestResult<()> {
        let result = verify_that!("123\n234", displays_as(eq("123\n345")));

        verify_that!(
            result,
            err(displays_as(contains_substring(indoc!(
                "
                  Actual: \"123\\n234\",
                    which displays as a string which isn't equal to \"123\\n345\"
                    Difference(-actual / +expected):
                     123
                    -234
                    +345
                "
            ))))
        )
    }
}