pretty_assertions 0.1.0

Overwrite `assert_eq!` with a drop-in replacement, adding a colorful diff.

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Pretty Assertions

When writing tests in Rust, you'll probably use assert_eq!(a, b) a lot.

If such a test fails, it will present all the details of a and b, but you have to spot, the differences yourself, which is not always straightforward, like here:

standard assertion

Wouldn't that task be much easier with a colorful diff?

pretty assertion

Yes it would. And you only need one line of code to make it happen — seriously:

// add the following line to the top of your crate root to
// overwrite `assert_eq!` with a colorful drop-in replacement
#[macro_use] extern crate pretty_assertions;

Ok, and don't forget to add the pretty_assertions dependency to Cargo.toml. Does that count as a line of code?.. ;-)


  • pretty_assertions is an ultra-thin wrapper around the difference crate, which does the heavy lifting. It replaces the assert_eq! macro with just about 22 lines of code.
  • The replacement is only effective in your own crate, not in other libraries you include.


This is the Rust code behind the screenshots above.

// uncomment the next line to make the assertions colorful:
//#[macro_use] extern crate pretty_assertions;

fn main() {
    #[derive(Debug, PartialEq)]
    struct Foo {
        lorem: &'static str,
        ipsum: u32,
        dolor: Result<String, String>,

    let x = Some(Foo { lorem: "Hello World!", ipsum: 42, dolor: Ok("hey".to_string())});
    let y = Some(Foo { lorem: "Hello Wrold!", ipsum: 42, dolor: Ok("hey ho!".to_string())});

    assert_eq!(x, y);


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