Double

Full-featured mocking library in Rust, including rich failure messages and argument matchers.

Documentation

Based off iredelmeier's initial mock implementation.

Double lets you mock Trait implementations so that you can track function call arguments and set return values or overrides functions at test time.

Here's a quick example:

extern crate double;

use double::Double;

trait Foo: Clone {
    fn expensive_fn(&self, x: i64, y: i64) -> i64;
}

#[derive(Clone)]
struct DoubleFoo {
    pub expensive_fn: Double<(i64, i64), i64>,
}

impl Foo for DoubleFoo {
    fn expensive_fn(&self, x: i64, y: i64) -> i64 {
        self.expensive_fn.call((x + 10, y))
    }
}

fn double_expensive_fn<T: Foo>(foo: &T, x: i64, y: i64) -> i64 {
    foo.expensive_fn(x, y) * 2
}

#[test]
fn doubles_return_value() {
    let mock = DoubleFoo { expensive_fn: Double::default() };

    mock.expensive_fn.return_value(1000);

    assert_eq!(double_expensive_fn(&mock, 1, 2), 2000);
}

#[test]
fn uses_correct_args() {
    let mock = DoubleFoo { expensive_fn: Double::default() };

    assert!(!mock.expensive_fn.called());

    double_expensive_fn(&mock, 1, 2);

    assert_eq!(mock.expensive_fn.num_calls(), 1);
    assert!(mock.expensive_fn.called_with((11, 2)));
}

More examples are available in the examples directory.

Credits

This library is based off iredelmeier's initial mocking implementation. Massive thanks to her implementation for inpsiring me to work on this. The repo for her library can be found here.

If you're interested in testing, check out her other repositories too!