Pretty Assertions

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

Usage

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:

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

Yep — and you only need one line of code to make it happen:

use pretty_assertions::{assert_eq, assert_ne};

Show the example behind the screenshots above.

// 1. add the `pretty_assertions` dependency to `Cargo.toml`.
// 2. insert this line at the top of each module, as needed
use pretty_assertions::{assert_eq, assert_ne};

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);
}

Semantic Versioning

The exact output of assertions is not guaranteed to be consistent over time, and may change between minor versions. The output of this crate is designed to be read by a human. It is not suitable for exact comparison, for example in snapshot testing.

This crate adheres to semantic versioning for publically exported crate items, except the private module, which may change between any version.

Tip

Specify it as [dev-dependencies] and it will only be used for compiling tests, examples, and benchmarks. This way the compile time of cargo build won't be affected!

Also add #[cfg(test)] to your use statements, like this:

#[cfg(test)]
use pretty_assertions::{assert_eq, assert_ne};

If you want to enforce usage of pretty_assertions macros over std, add the following to clippy.toml:

disallowed-macros = [
  { path = "std::assert_ne", reason = "use `pretty_assertions::assert_ne` instead" },
  { path = "std::assert_eq", reason = "use `pretty_assertions::assert_eq` instead" },
  { path = "std::assert_matches::assert_matches", reason = "use `pretty_assertions::assert_matches` instead" },
]

Notes

• Since Rust 2018 edition, you need to declare use pretty_assertions::{assert_eq, assert_ne}; per module. Before you would write #[macro_use] extern crate pretty_assertions;.
• The replacement is only effective in your own crate, not in other libraries you include.
• assert_ne is also switched to multi-line presentation, but does not show a diff.
• Under Windows, the terminal state is modified to properly handle VT100 escape sequences, which may break display for certain use cases.
• The minimum supported rust version (MSRV) is 1.35.0

no_std support

For no_std support, disable the std feature and enable the alloc feature:

# Cargo.toml
pretty_assertions = { version= "...", default-features = false, features = ["alloc"] }

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Development

• Cut a new release by creating a GitHub release with tag. Crate will be built and uploaded to crates.io by GHA.