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/// Asserts that expression returns [`Err(E)`] variant. /// /// ## Uses /// /// Assertions are always checked in both debug and release builds, and cannot be disabled. /// See [`debug_assert_err!`] for assertions that are not enabled in release builds by default. /// /// ## Custom messages /// /// This macro has a second form, where a custom panic message can be provided /// with or without arguments for formatting. See [`std::fmt`] for syntax for this form. /// /// ## Examples /// /// ```rust /// # #[macro_use] extern crate claim; /// # fn main() { /// let res: Result<i32, ()> = Err(()); /// /// assert_err!(res); /// /// // With custom messages /// assert_err!(res, "we are checking if there was an error with {:?}", res); /// # } /// ``` /// /// `Ok(T)` variant will cause panic: /// /// ```rust,should_panic /// # #[macro_use] extern crate claim; /// # fn main() { /// let res: Result<i32, ()> = Ok(42); /// /// assert_err!(res); // Will panic /// # } /// ``` /// /// [`std::fmt`]: https://doc.rust-lang.org/std/fmt/index.html /// [`Err(E)`]: https://doc.rust-lang.org/core/result/enum.Result.html#variant.Err /// [`debug_assert_err!`]: ./macro.debug_assert_err.html #[macro_export] macro_rules! assert_err { ($cond:expr,) => { $crate::assert_err!($cond); }; ($cond:expr) => { match $cond { Ok(t) => { panic!("assertion failed, expected Err(..), got Ok({:?})", t); }, Err(e) => e, } }; ($cond:expr, $($arg:tt)+) => { match $cond { Ok(t) => { panic!("assertion failed, expected Err(..), got Ok({:?}): {}", t, format_args!($($arg)+)); }, Err(e) => e, } }; } /// Asserts that expression returns [`Err(E)`] variant in runtime. /// /// Like [`assert_err!`], this macro also has a second version, /// where a custom panic message can be provided. /// /// ## Uses /// /// See [`debug_assert!`] documentation for possible use cases. /// The same applies to this macro. /// /// [`Err(E)`]: https://doc.rust-lang.org/core/result/enum.Result.html#variant.Err /// [`debug_assert!`]: https://doc.rust-lang.org/std/macro.debug_assert.html /// [`assert_err!`]: ./macro.assert_err.html #[macro_export] macro_rules! debug_assert_err { ($($arg:tt)*) => (if cfg!(debug_assertions) { $crate::assert_err!($($arg)*); }) } #[cfg(test)] #[cfg(not(has_private_in_public_issue))] mod tests { #[test] #[should_panic(expected = "assertion failed, expected Err(..), got Ok(42)")] fn default_panic_message() { let res: Result<i32, ()> = Ok(42); assert_err!(res); } #[test] #[should_panic( expected = "assertion failed, expected Err(..), got Ok(42): we are checking if there was an error with Ok(42)" )] fn custom_panic_message() { let res: Result<i32, ()> = Ok(42); assert_err!(res, "we are checking if there was an error with {:?}", res); } #[test] fn does_not_require_err_debug() { enum Foo { Bar, } let res: Result<i32, Foo> = Err(Foo::Bar); let _ = assert_err!(res); } }