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Yare ⛵

A lean procedural macro based parameterized testing library. Run a test case with many different inputs. Patameterized test cases are defined using the 'parameterized' attribute instead of a default 'test' attribute.

Features

  • Parameterized Testing: Specify different inputs to test multiple scenarios with a single test definition.
  • Be flexible: Arguments provided to parameterized test cases are expressions.
  • Works out of the box: Works with any Rust version out of the box. No custom test harness necessary.
  • Concise yet comprehensive: Minimalstic doesn't need to mean 'featureless'.
  • Familiar syntax: Maintains code readability with familiar Rustic syntax.
  • Promotes : Each test case has a user defined name which can be referred back to, and can be used to run individual test cases.
  • Battle tested: Used for years in tests of the cargo-msrv, bisector and rust-releases crates (amongst others).

Table of contents

Examples (back to top)

A first example

fn add5<T: Into<u32>>(component: T) -> u32 {
    component.into() + 5
}

#[cfg(test)]
mod tests {
    use super::*;
    use yare::parameterized;

    #[parameterized(
      zero_plus_five = { 0, 5 },
      one_plus_five = { 1, 6 },
      two_plus_five = { 2, 7 },
    )]
    fn test_add5(input: u16, expected: u32) {
        assert_eq!(add5(input), expected);
    }
}

An example with values

enum Fruit {
    Apple,
    Bramble(BrambleFruit),
    Pear,
}

trait NameOf {
    fn name_of(&self) -> &str;
}

impl NameOf for Fruit {
    fn name_of(&self) -> &str {
        match self {
            Fruit::Apple => "apple",
            Fruit::Bramble(fruit) => fruit.name_of(),
            Fruit::Pear => "pear",
        }
    }
}

enum BrambleFruit {
    Blackberry,
}

impl NameOf for BrambleFruit {
    fn name_of(&self) -> &str {
        match self {
            BrambleFruit::Blackberry => "blackberry",
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use yare::parameterized;

    #[parameterized(
      apple = { Fruit::Apple, "apple" },
      pear = { Fruit::Pear, "pear" },
      blackberry = { Fruit::Bramble(BrambleFruit::Blackberry), "blackberry" },
    )]
    fn a_fruity_test(fruit: Fruit, name: &str) {
        assert_eq!(fruit.name_of(), name)
    }
}

Arguments are expressions (back to top)

While the arguments above were simple values, any expression can be used as argument in a test case.

Example

In the example below, we roll the dice 3 times, to generate a seed for later roll_dice function calls. The first argument seed1 is a function call to roll_dice. This randomness function is seeded with value 0. The second argument seed2 is a block expression. In the expression the roll_dice function is called twice. The test itself takes the maximum of seed1 and seed2, rolls the die 1000 times, and checks that all values are valid for a d6 die.

use std::sync::atomic::{AtomicU32, Ordering};
use yare::parameterized;

#[parameterized(
  // A complex input for the sake of showing that inputs are expressions...
  seeding_randomness_with_two_dice_rolls = 
  {
    roll_dice(&AtomicU32::new(0)),                              // <- This is an expression (a function call)
    {                                                           // <- This is also an expression (a block expression)
      let from_half = roll_dice( &AtomicU32::new(u32::MAX / 2));
      let from_max = roll_dice( &AtomicU32::new(u32::MAX));
      
      u8::min(from_half, from_max)
    }
  }
)]
fn dicey(seed1: u8, seed2: u8) {
    // Creating a base seed in a complicated way for the sake of it.
    let max = u8::max(seed1, seed2);
    let seed = AtomicU32::new(u32::from(max));

    let out_of_bounds_values = (0..1000)         // roll the dice 1000 times
        .map(|_| roll_dice(&seed))
        .find(|value| !(1..=6).contains(value)); // check that the outputs of the dice are just 1, 2, 3, 4, 5 or 6. 

    assert!(out_of_bounds_values.is_none());
}

Custom test macro (e.g. tokio::test) (back to top)

By default, the code generation step of the parameterized attribute will generate test cases marked with a #[test] attribute. For example, the add5 test from the examples would generate something like:

#[cfg(test)]
mod tests {
    use super::*;
    use yare::parameterized;

    // Approximate generated code from add5 example:
    #[cfg(test)]
    mod add5 {
        use super::*;

        #[test]
        fn zero_plus_five() {
            let input: u16 = 0;
            let expected: u32 = 5;
            assert_eq!(add5(input), expected);
        }

        #[test]
        fn one_plus_five() {
            let input: u16 = 1;
            let expected: u32 = 6;
            assert_eq!(add5(input), expected);
        }

        #[test]
        fn two_plus_five() {
            let input: u16 = 2;
            let expected: u32 = 7;
            assert_eq!(add5(input), expected);
        }
    }
}

However, sometimes a different test macro is desired. An example is when writing tests for projects which depend on tokio. For this, you may want to use #[tokio::test] (it also requires the test function to also have the async qualifier).

In Yare, it is possible to specify a custom test macro. To do so, you may add the #[test_macro(...)] attribute after a #[parameterized] attribute.

Custom test macro example: tokio::test

use yare::parameterized;

#[parameterized(
    zero_wait = { 0, 0 },
    show_paused = { 500, 0 },
)]
#[test_macro(tokio::test(start_paused = true))]
async fn test(wait: u64, time_elapsed: u128) {
    let start = std::time::Instant::now();
    tokio::time::sleep(tokio::time::Duration::from_millis(wait)).await;

    assert_eq!(start.elapsed().as_millis(), time_elapsed);
}

Gotchas:

  • The #[test_macro(...)] must always be specified after a #[parameterized(...)] attribute.
  • Only one #[test_macro(...)] attribute per parameterized test function is allowed.
  • While you can rename the parameterized attribute using import aliassing ( e.g. use yare::parameterized as pm), the test_macro attribute cannot be renamed, since it's not actually defined as a separate macro. Instead, the parameterized macro parses this attribute as well.

Return types (back to top)

Yare supports specifying a return type for a parameterized test function.

Note that the underlying test attribute must also have support for return types. By default, Yare generates individual test cases decorated with the familiar test attribute, which is included with any Rust distribution by default.

Example

use yare::parameterized;

#[parameterized(
  ok = { Ok(0) },
  // err = {  Err("noes!".to_string()) }, <-- enabling this would result in a failed test, since the error code will not be an `ErrorCode::Success`. See the `Termination` trait for more.
)]
fn test(value: Result<u32, String>) -> Result<(), String> {
    let v = value?;

    assert_eq!(v.unwrap(), 0);
}

Function qualifiers (back to top)

Yare supports the following function qualifiers: const, async, unsafe and extern. This is particularly useful if you use #[parameterized(...)] with a custom test macro such as tokio::test, instead of the built-in test macro.

Example

use yare::parameterized;

#[parameterized(
  purple = { & [128, 0, 128] },
  orange = { & [255, 127, 0] },
)]
const extern "C" fn has_reds(streamed_color: &[u8]) {
    assert!(streamed_color.first().is_some());
}

Globally importing parameterized (back to top)

If you prefer not to import this library (with use yare::parameterized;) in every test module, you can put the following snippet at the top of your crate root:

#[cfg(test)]
#[macro_use]
extern crate yare;

Alternatives (back to top)

If Yare is not quite what you're looking for, there are some alternatives:

License (back to top)

Licensed under either of Apache License, Version 2.0 or MIT license at your option.


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