Fixture-based test framework for Rust

Introduction

rstest uses procedural macros to help you on writing fixtures and table-based tests. To use it, add the following lines to your Cargo.toml file:

[dev-dependencies]
rstest = "0.7.0"

Fixture

The core idea is that you can inject your test dependencies by passing them as test arguments. In the following example, a fixture is defined and then used in two tests, simply providing it as an argument:

use rstest::*;

#[fixture]
pub fn fixture() -> u32 { 42 }

#[rstest]
fn should_success(fixture: u32) {
    assert_eq!(fixture, 42);
}

#[rstest]
fn should_fail(fixture: u32) {
    assert_ne!(fixture, 42);
}

Parametrize

You can also inject values in some other ways. For instance, you can create a set of tests by simply providing the injected values for each case: rstest will generate an independent test for each case.

use rstest::rstest;

#[rstest(input, expected,
    case(0, 0),
    case(1, 1),
    case(2, 1),
    case(3, 2),
    case(4, 3)
)]
fn fibonacci_test(input: u32, expected: u32) {
    assert_eq!(expected, fibonacci(input))
}

Running cargo test in this case executes five tests:

running 5 tests
test fibonacci_test::case_1 ... ok
test fibonacci_test::case_2 ... ok
test fibonacci_test::case_3 ... ok
test fibonacci_test::case_4 ... ok
test fibonacci_test::case_5 ... ok

test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

If you need to just providing a bunch of values for which you need to run your test, you can use var => [list, of, values] syntax:

use rstest::rstest;

#[rstest(
    value => [None, Some(""), Some("    ")]
)]
fn should_be_invalid(value: Option<&str>) {
    assert!(!valid(value))
}

Or create a matrix test by using list of values for some variables that will generate the cartesian product of all the values.

Use Parametrize definition in more tests

If you need to use a test list for more than one test you can use rstest_reuse crate. With this helper crate you can define a template and use it everywhere .

use rstest::rstest;
use rstest_reuse::{self, *};

#[template]
#[rstest(a,  b,
    case(2, 2),
    case(4/2, 2),
    )
]
fn two_simple_cases(a: u32, b: u32) {}

#[apply(two_simple_cases)]
fn it_works(a: u32, b: u32) {
    assert!(a == b);
}

See rstest_reuse for more dettails.

Async

rstest provides out of the box async support. Just mark your test function as async and it'll use #[async-std::test] to annotate it. This feature can be really useful to build async parametric tests using a tidy syntax:

use rstest::*;

#[rstest(expected, a, b,
    case(5, 2, 3),
    #[should_panic]
    case(42, 40, 1)
)]
async fn my_async_test(expected: u32, a: u32, b: u32) {
    assert_eq!(expected, async_sum(a, b).await);
}

Currently only async-std is supported out of the box. But if you need to use another runtime that provide it's own test attribute (i.e. tokio::test or actix_rt::test) you can use it in your async test like described in Inject Test Attribute.

To use this feature, you need to enable attributes in the async-std features list in your Cargo.toml:

async-std = { version = "1.5", features = ["attributes"] }

Inject Test Attribute

If you would like to use another test attribute for your test you can simply indicate it in your test function's attributes. For instance if you want to test some async function with use actix_rt::test attribute you can just write:

use rstest::*;
use actix_rt;
use std::future::Future;

#[rstest(a, result,
    case(2, async { 4 }),
    case(21, async { 42 })
)]
#[actix_rt::test]
async fn my_async_test(a: u32, result: impl Future<Output=u32>) {
    assert_eq!(2 * a, result.await);
}

Just the attributes that ends with test (last path segment) can be injected.

Complete Example

All these features can be used together with a mixture of fixture variables, fixed cases and bunch of values. For instance, you might need two test cases which test for panics, one for a logged in user and one for a guest user.

use rstest::*;

#[fixture]
fn repository() -> InMemoryRepository {
    let mut r = InMemoryRepository::default();
    // fill repository with some data
    r
}

#[fixture]
fn alice() -> User {
    User::logged("Alice", "2001-10-04", "London", "UK")
}

#[rstest(user,
    case::authed_user(alice()), // We can use `fixture` also as standard function
    case::guest(User::Guest),   // We can give a name to every case : `guest` in this case
                                // and `authed_user`
    query => ["     ", "^%$#@!", "...." ]
)]
#[should_panic(expected = "Invalid query error")] // We whould test a panic
fn should_be_invalid_query_error(repository: impl Repository, user: User, query: &str) {
    repository.find_items(&user, query).unwrap();
}

This example will generate exactly 6 tests grouped by 2 different cases:

running 6 tests
test should_be_invalid_query_error::case_1_authed_user::query_1 ... ok
test should_be_invalid_query_error::case_2_guest::query_2 ... ok
test should_be_invalid_query_error::case_2_guest::query_3 ... ok
test should_be_invalid_query_error::case_1_authed_user::query_2 ... ok
test should_be_invalid_query_error::case_1_authed_user::query_3 ... ok
test should_be_invalid_query_error::case_2_guest::query_1 ... ok

test result: ok. 6 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

More

Is that all? Not quite yet!

A fixture can be injected by another fixture and they can be called using just some of its arguments.

#[fixture(name="Alice", age=22)]
fn user(name: &str, age: u8) -> User {
    User::new(name, age)
}

#[rstest]
fn is_alice(user: User) {
    assert_eq!(user.name(), "Alice")
}

#[rstest]
fn is_22(user: User) {
    assert_eq!(user.age(), 22)
}

#[rstest(user("Bob"))]
fn is_bob(user: User) {
    assert_eq!(user.name(), "Bob")
}

#[rstest(user("", 42))]
fn is_42(user: User) {
    assert_eq!(user.age(), 42)
}

As you noted you can provide default values without the need of a fixture to define it.

Finally if you need tracing the input values you can just add the trace attribute to your test to enable the dump of all input variables.

#[rstest(
    number, name, tuple,
    case(42, "FortyTwo", ("minus twelve", -12)),
    case(24, "TwentyFour", ("minus twentyfour", -24))
    ::trace //This attribute enable traceing
)]
fn should_fail(number: u32, name: &str, tuple: (&str, i32)) {
    assert!(false); // <- stdout come out just for failed tests
}

running 2 tests
test should_fail::case_1 ... FAILED
test should_fail::case_2 ... FAILED

failures:

---- should_fail::case_1 stdout ----
------------ TEST ARGUMENTS ------------
number = 42
name = "FortyTwo"
tuple = ("minus twelve", -12)
-------------- TEST START --------------
thread 'should_fail::case_1' panicked at 'assertion failed: false', src/main.rs:64:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.

---- should_fail::case_2 stdout ----
------------ TEST ARGUMENTS ------------
number = 24
name = "TwentyFour"
tuple = ("minus twentyfour", -24)
-------------- TEST START --------------
thread 'should_fail::case_2' panicked at 'assertion failed: false', src/main.rs:64:5


failures:
    should_fail::case_1
    should_fail::case_2

test result: FAILED. 0 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out

In case one or more variables don't implement the Debug trait, an error is raised, but it's also possible to exclude a variable using the notrace(var,list,that,not,implement,Debug) attribute.

You can learn more on Docs and find more examples in resources directory and in rs8080 which uses this module in-depth.

Changelog

See CHANGELOG.md

License

Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or license-apache-link)

• MIT license LICENSE-MIT or license-MIT-link at your option.