mrcosta / mockers

Mocking library for Rust

master	0.13.1

Mockers

Mocking library for Rust.

Inspired by Google Mock library for C++.

User Guide

Note: breaking change

Versions before 0.10.0 were implemented as compiler plugin and used syntex crate for parsing. Compiler plugins are now deprecated, and syntex crate is not maintained anymore.

Version 0.10.0 migrated from compiler plugin implementation to usage of proc_macro_attribute feature. Since this feature isn't supported in stable Rust yet, mockers is only available on unstable at the moment. It is possible that support for stable Rust will be implemented even before proc_macro_attribute feature stabilization.

In trivial cases migration of your tests to new mockers version is as simple as replacing #[derive(Mock)] with #[mocked].

In version 0.12.0 macro attribute was renamed from "derive_mock" to "mocked". "derive_mock" attribute is still available and is alias to "mocked", but it will eventually be deprecated.

Limitations

For now it is not a full-featured mocking library, but just a prototype to gather feedback. For example, only methods with four or fewer arguments are supported, non-'static lifetimes are not supported and so on.

Features are added on demand, so feel free to contact me and explain your needs.

Mocking magic is implemented using proc_macro_attribute attribute which is only available on nightly Rust (it was tested to work with 1.30.0-nightly (67390c0c3 2018-08-14)). Working on stable Rust will be supported later.

Usage at a glance

This is a very short introduction to show what is possible and how it looks. Read User Guide for details.

We will use nightly Rust in this example for simplicity.

For multirust, run the following command:

$ multirust override nightly

Or if you're using rustup:

$ rustup override set nightly

Cargo.toml:

[dev-dependencies]
mockers = "0.13.1"
mockers_derive = "0.13.1"

src/lib.rs:

#![feature(use_extern_macros)]

#[cfg(test)] extern crate mockers_derive;

#[cfg(test)] use mockers_derive::mocked;

#[cfg_attr(test, mocked)]
pub trait AirConditioner {
    fn make_hotter(&mut self, by: i16);
    fn make_cooler(&mut self, by: i16);
    fn get_temperature(&self) -> i16;
}

pub fn set_temperature_20(cond: &mut AirConditioner) {
    let t = cond.get_temperature();
    if t < 20 {
        cond.make_hotter(20 + t);
    } else {
        cond.make_cooler(t - 20);
    }
}

#[cfg(test)]
mod test {
  use super::*;
  use mockers::Scenario;

  #[test]
  fn test_set_temperature_20() {
      let scenario = Scenario::new();
      let mut cond = scenario.create_mock_for::<AirConditioner>();

      scenario.expect(cond.get_temperature_call().and_return(16));
      scenario.expect(cond.make_hotter_call(4).and_return(()));

      set_temperature_20(&mut cond);
  }
}

Run tests:

$ cargo test
   Compiling air v0.1.0 (file:///Users/kriomant/Temp/air)
     Running target/debug/air-b2c5f8b6920cb30a

running 1 test
test test::test_set_temperature_20 ... FAILED

failures:

---- test::test_set_temperature_20 stdout ----
	thread 'test::test_set_temperature_20' panicked at '

error: unexpected call to `AirConditioner#0.make_hotter(36)`

note: here are active expectations for AirConditioner#0.make_hotter

  expectation `AirConditioner#0.make_hotter(4)`:
    arg #0: 36 is not equal to 4

'
note: Run with `RUST_BACKTRACE=1` for a backtrace.


failures:
    test::test_set_temperature_20

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured

error: test failed

License

Copyright © 2016 Mikhail Trishchenkov

Distributed under the MIT License.