Automock - crate for mocking anything

Rust Users Forum2026-10-29 23:150 views

Hi! I'd like to share a project I've been working on in my free time for the past year.
It's a crate for mocking functions, traits and structs.

https://crates.io/crates/automock

#[automock::mock] trait Trait { fn work(&self, v: i32) -> i32; } #[test] fn test() { // Arrange let mut mock = TraitMock::new(); mock.setup().work(1).returns_once(2); // Act let result = mock.work(1); // Assert assert_eq!(result, 2); mock.verify_calls(); }

It already covers almost all of mockall and faux crates features (two of the most widely used crates for mocking), so I'll focus on some of its advantages in this post:

Partial mocking - you can configure mocked function to use its original implementation in certain scenarios:

#[automock::mock] trait Trait { fn work(&self, v: i32) -> i32 { 4 // base implementation } } #[test] fn main() { // Arrange let mut mock = TraitMock::new(); mock.setup() .work(1).returns_once(2) .work(3).call_base(); // Act let first = mock.work(1); let second = mock.work(3); // uses base implementation // Assert assert_eq!(first, 2); assert_eq!(second, 4); mock.verify_calls(); }

Static functions mocking - any static function can be mocked, whether it's standalone or associated function:

#[automock::mock] fn work(v: i32) -> i32 { v } #[automock::mock] trait Trait { fn work(v: i32) -> i32; } fn use_trait<T: Trait>(v: i32) -> i32 { T::work(v) } #[test] fn test() { // Arrange work::setup(1).returns_once(2); TraitMock::static_setup().work(3).returns_once(4); // Act let first = work(1); let second = use_trait::<TraitMock>(3); // Assert assert_eq!(first, 2); assert_eq!(second, 4); work::verify_calls(); TraitMock::verify_static_calls(); }

A single #[mock] attribute for everything - you can apply it to traits, structs, struct implementations, trait on struct implementations or static functions. No need for mock!, #[concretize], #[double], #[faux::create]or #[faux::methods] attributes.
Better generics: support for lifetimes and default generic values. Here's an example of monstrous trait implementation that it can mock (click for more details)