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 = "0.19.0"

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]
#[case(0, 0)]
#[case(1, 1)]
#[case(2, 1)]
#[case(3, 2)]
#[case(4, 3)]
fn fibonacci_test(#[case] input: u32, #[case] 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 #[values(list, of, values)] argument attribute:

use rstest::rstest;

#[rstest]
fn should_be_invalid(
    #[values(None, Some(""), Some("    "))]
    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]
#[case(2, 2)]
#[case(4/2, 2)]
fn two_simple_cases(#[case] a: u32, #[case] b: u32) {}

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

See rstest_reuse for more details.

Feature flagged cases

In case you want certain test cases to only be present if a certain feature is enabled, use #[cfg_attr(feature = …, case(…))]:

use rstest::rstest;

#[rstest]
#[case(2, 2)]
#[cfg_attr(feature = "frac", case(4/2, 2))]
#[case(4/2, 2)]
fn it_works(#[case] a: u32, #[case] b: u32) {
    assert!(a == b);
}

This also works with rstest_reuse.

Magic Conversion

If you need a value where its type implement FromStr() trait you can use a literal string to build it:

# use rstest::rstest;
# use std::net::SocketAddr;
#[rstest]
#[case("1.2.3.4:8080", 8080)]
#[case("127.0.0.1:9000", 9000)]
fn check_port(#[case] addr: SocketAddr, #[case] expected: u16) {
    assert_eq!(expected, addr.port());
}

You can use this feature also in value list and in fixture default value.

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]
#[case(5, 2, 3)]
#[should_panic]
#[case(42, 40, 1)]
async fn my_async_test(#[case] expected: u32, #[case] a: u32, #[case] 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 its 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"] }

If your test input is an async value (fixture or test parameter) you can use #[future] attribute to remove impl Future<Output = T> boilerplate and just use T:

use rstest::*;
#[fixture]
async fn base() -> u32 { 42 }

#[rstest]
#[case(21, async { 2 })]
#[case(6, async { 7 })]
async fn my_async_test(#[future] base: u32, #[case] expected: u32, #[future] #[case] div: u32) {
    assert_eq!(expected, base.await / div.await);
}

As you noted you should .await all future values and this sometimes can be really boring. In this case you can use #[future(awt)] to awaiting an input or annotating your function with #[awt] attributes to globally .await all your future inputs. Previous code can be simplified like follow:

use rstest::*;
# #[fixture]
# async fn base() -> u32 { 42 }
#[rstest]
#[case(21, async { 2 })]
#[case(6, async { 7 })]
#[awt]
async fn global(#[future] base: u32, #[case] expected: u32, #[future] #[case] div: u32) {
    assert_eq!(expected, base / div);
}
#[rstest]
#[case(21, async { 2 })]
#[case(6, async { 7 })]
async fn single(#[future] base: u32, #[case] expected: u32, #[future(awt)] #[case] div: u32) {
    assert_eq!(expected, base.await / div);
}

Files path as input arguments

If you need to create a test for each file in a given location you can use #[files("glob path syntax")] attribute to generate a test for each file that satisfy the given glob path.

#[rstest]
fn for_each_file(#[files("src/**/*.rs")] #[exclude("test")] path: PathBuf) {
    assert!(check_file(&path))
}

The default behavior is to ignore the files that start with ".", but you can modify this by use #[include_dot_files] attribute. The files attribute can be used more than once on the same variable, and you can also create some custom exclusion rules with the #[exclude("regex")] attributes that filter out all paths that verify the regular expression.

Default timeout

You can set a default timeout for test using the RSTEST_TIMEOUT environment variable. The value is in seconds and is evaluated on test compile time.

Test `#[timeout()]`

You can define an execution timeout for your tests with #[timeout(<duration>)] attribute. Timeout works both for sync and async tests and is runtime agnostic. #[timeout(<duration>)] take an expression that should return a std::time::Duration. Follow a simple async example:

use rstest::*;
use std::time::Duration;

async fn delayed_sum(a: u32, b: u32,delay: Duration) -> u32 {
    async_std::task::sleep(delay).await;
    a + b
}

#[rstest]
#[timeout(Duration::from_millis(80))]
async fn single_pass() {
    assert_eq!(4, delayed_sum(2, 2, ms(10)).await);
}

In this case test pass because the delay is just 10 milliseconds and timeout is 80 milliseconds.

You can use timeout attribute like any other attribute in your tests, and you can override a group timeout with a case specific one. In the follow example we have 3 tests where first and third use 100 milliseconds but the second one use 10 milliseconds. Another valuable point in this example is to use an expression to compute the duration.

fn ms(ms: u32) -> Duration {
    Duration::from_millis(ms.into())
}

#[rstest]
#[case::pass(ms(1), 4)]
#[timeout(ms(10))]
#[case::fail_timeout(ms(60), 4)]
#[case::fail_value(ms(1), 5)]
#[timeout(ms(100))]
async fn group_one_timeout_override(#[case] delay: Duration, #[case] expected: u32) {
    assert_eq!(expected, delayed_sum(2, 2, delay).await);
}

If you want to use timeout for async test you need to use async-timeout feature (enabled by default).

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]
#[case(2, async { 4 })]
#[case(21, async { 42 })]
#[actix_rt::test]
async fn my_async_test(#[case] a: u32, #[case] #[future] result: u32) {
    assert_eq!(2 * a, result.await);
}

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

Use `#[once]` Fixture

If you need to a fixture that should be initialized just once for all tests you can use #[once] attribute. rstest call your fixture function just once and return a reference to your function result to all your tests:

#[fixture]
#[once]
fn once_fixture() -> i32 { 42 }

#[rstest]
fn single(once_fixture: &i32) {
    // All tests that use once_fixture will share the same reference to once_fixture() 
    // function result.
    assert_eq!(&42, once_fixture)
}

Complete Example

All these features can be used together with a mixture of fixture variables, fixed cases and a 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]
#[case::authorized_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 `authorized_user`
#[should_panic(expected = "Invalid query error")] // We would test a panic
fn should_be_invalid_query_error(
    repository: impl Repository,
    #[case] user: User,
    #[values("     ", "^%$some#@invalid!chars", ".n.o.d.o.t.s.")] 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_authorized_user::query_1_____ - should panic ... ok
test should_be_invalid_query_error::case_2_guest::query_2_____someinvalid_chars__ - should panic ... ok
test should_be_invalid_query_error::case_1_authorized_user::query_2_____someinvalid_chars__ - should panic ... ok
test should_be_invalid_query_error::case_2_guest::query_3____n_o_d_o_t_s___ - should panic ... ok
test should_be_invalid_query_error::case_1_authorized_user::query_3____n_o_d_o_t_s___ - should panic ... ok
test should_be_invalid_query_error::case_2_guest::query_1_____ - should panic ... ok

test result: ok. 6 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

Note that the names of the values try to convert the input expression in a Rust valid identifier name to help you find which tests fail.

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]
fn user(#[default("Alice")] name: &str, #[default(22)] 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]
fn is_bob(#[with("Bob")] user: User) {
    assert_eq!(user.name(), "Bob")
}

#[rstest]
fn is_42(#[with("", 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]
#[case(42, "FortyTwo", ("minus twelve", -12))]
#[case(24, "TwentyFour", ("minus twentyfour", -24))]
#[trace] //This attribute enable tracing
fn should_fail(#[case] number: u32, #[case] name: &str, #[case] 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] argument attribute.

You can learn more on Docs and find more examples in tests/resources directory.