Crate rstest_reuse

source ·
Expand description

Reuse rstest’s parametrized cases

This crate give a way to define a tests set and apply them to every case you need to test.

With rstest crate you can define a tests list but if you want to apply the same tests to another test function you must rewrite all cases or write some macros that do the job. Both solutions have some drawbreak:

  • introduce duplication
  • macros makes code harder to read and shift out the focus from tests core

The aim of this crate is solve this problem. rstest_reuse expose two attributes:

  • #[template]: to define a template
  • #[apply]: to apply a defined template to create tests

Here is a simple example:

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

// Here we define the template. This define
// * The test list name to `two_simple_cases`
// * cases: here two cases that feed the `a`, `b` values
#[case(2, 2)]
#[case(4/2, 2)]
fn two_simple_cases(#[case] a: u32,#[case] b: u32) {}

// Here we apply the `two_simple_cases` template: That is expanded in
// #[rstest]
// #[case(2, 2)]
// #[case(4/2, 2)]
// fn it_works(#[case] a: u32,#[case] b: u32) {
//     assert!(a == b);
// }
fn it_works(a: u32, b: u32) {
    assert!(a == b);

// Here we reuse the `two_simple_cases` template to create two
// other tests
fn it_fail(a: u32, b: u32) {
    assert!(a != b);

If we run cargo test we have:

    Finished test [unoptimized + debuginfo] target(s) in 0.05s
     Running target/debug/deps/playground-8a1212f8b5eb00ce

running 4 tests
test it_fail::case_1 ... FAILED
test it_works::case_1 ... ok
test it_works::case_2 ... ok
test it_fail::case_2 ... FAILED


---- it_fail::case_1 stdout ----
thread 'it_fail::case_1' panicked at 'assertion failed: a != b', src/
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- it_fail::case_2 stdout ----
thread 'it_fail::case_2' panicked at 'assertion failed: a != b', src/


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

error: test failed, to rerun pass '--bin playground'

Simple and neat!

Note that if the test arguments names match the template’s ones you can don’t repeate the arguments attributes.

Composition and Values

If you need to add some cases or values when apply a template you can leverage on composition. Here a simple example:

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

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

// Here we add a new case and an argument in a value list:
#[case(9/3, 3)]
fn it_works(a: u32, b: u32, #[values("a", "b")] t: &str) {
    assert!(a == b);

cargo test runs 6 tests:

running 6 tests
test it_works::case_1::t_2 ... ok
test it_works::case_2::t_2 ... ok
test it_works::case_2::t_1 ... ok
test it_works::case_3::t_2 ... ok
test it_works::case_3::t_1 ... ok
test it_works::case_1::t_1 ... ok

Template can also used for #[values] and #[with] arguments if you need:

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

fn base(#[with(42)] fix: u32, #[values(1,2,3)] v: u32) {}

fn fix(#[default(0)] inner: u32) -> u32 {

fn use_it_with_fixture(fix: u32, v: u32) {
    assert!(fix%v == 0);

fn use_it_without_fixture(v: u32) {
    assert!(24 % v == 0);

cargo test runs 6 tests:

running 6 tests
test use_it_with_fixture::v_1 ... ok
test use_it_without_fixture::v_1 ... ok
test use_it_with_fixture::v_3 ... ok
test use_it_without_fixture::v_2 ... ok
test use_it_without_fixture::v_3 ... ok
test use_it_with_fixture::v_2 ... ok


use rstest_reuse at the top of your crate

You should add use rstest_reuse at the top of your crate:

use rstest_reuse;

This is due rstest_reuse::template define a macro that need to call a rstest_reuse’s macro. I hope to remove this in the future but for now we should live with it.

Note that

use rstest_reuse::*;

is not enougth: this statment doesn’t include rstest_reuse but just its public items.


This crate is in developer stage. I don’t know if I’ll include it in rstest or changing some syntax in the future.

I did’t test it in a lot of cases: if you have some cases where it doesn’t works file a ticket on rstest

Attribute Macros

  • Apply a defined template. The function signature should satisfy the template attributes but can also add some other fixtures. Example:
  • Define a template where the name is given from the function name. This attribute register all attributes. The function signature don’t really mater but to make it clear is better that you use a signature like if you’re wrinting a standard rstest.