The ! indicates that assert_eq is a macro call. Usage example: https://doc.rust-lang.org/std/macro.assert_eq!.html https://doc.rust-lang.org/std/macro.assert_e

The ! indicates that assert_eq is a macro call. Usage example: https://doc.rust-lang.org/std/macro.assert_eq!.html https://doc.rust-lang.org/std/macro.assert_eq!.html