Reuse rstest's parametrized cases

:warning: Version 0.2.0 introduce a breaking change

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:

• intruduce 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_resuse 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
#[template]
#[rstest]
#[case(2, 2)]
#[case(4/2, 2)]
// Define a and b as cases arguments
fn two_simple_cases(#[case] a: u32, #[case] b: u32) {}
// Here we apply the `two_simple_cases` template: That is expanded in
// #[template]
// #[rstest]
// #[case(2, 2)]
// #[case(4/2, 2)]
// fn it_works(#[case] a: u32,#[case] b: u32) {
//     assert!(a == b);
// }
#[apply(two_simple_cases)]
fn it_works(a: u32, b: u32) {
    assert!(a == b);
}
// Here we reuse the `two_simple_cases` template to create two 
// other tests
#[apply(two_simple_cases)]
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
failures:
---- it_fail::case_1 stdout ----
-------------- TEST START --------------
thread 'it_fail::case_1' panicked at 'assertion failed: a != b', src/main.rs:34:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
---- it_fail::case_2 stdout ----
-------------- TEST START --------------
thread 'it_fail::case_2' panicked at 'assertion failed: a != b', src/main.rs:34:5
failures:
    it_fail::case_1
    it_fail::case_2
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:

#[template]
#[rstest]
#[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:
#[apply(base)]
#[case(9/3, 3)]
fn it_works(a: u32, b: u32, #[values("a", "b")] t: &str) {
    assert!(a == b);
    assert!("abcd".contains(t))
}

run 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:

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

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

#[apply(base)]
fn use_it_with_fixture(fix: u32, v: u32) {
    assert!(fix%v == 0);
}

#[apply(base)]
fn use_it_without_fixture(v: u32) {
    assert!(24 % v == 0);
}

Run also 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

Cavelets

use rstest_resuse at the top of your crate

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

#[cfg(test)]
use rstest_reuse;

This is due rstest_reuse::template define a macro that need to call a rstest_resuse'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.

Define template before apply it

template attribute define a macro that apply will use. Macro in rust are expanded in a single depth-first, lexical-order traversal of a crate’s source, that means the template definition should be allways before the apply.

Tag modules with #[macro_use]

If you define a template in a module and you plan to use it outside the module, you should lift it by marking the module with the #[macro_use] attribute. This attribute makes your template visible outside this module but not at the upper level (Rust's macro docs). When a template is defined, you can use it in all submodules that follow the definition!

Let's take a look at this example, which won't work: \ lib.rs:

/// This module contains some test.
mod run_tests;

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

The following won't work, since the declaration of the two_simple_cases macro happened after the definition of the module: \ run_tests.rs:

use super::*;

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

If we move mod run_tests; below the template, everything works fine.

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

mod run_tests;

If you plan to spread your templates accross multiple modules and you use different names for each template, you can also consider to add the global attribute !#[macro_use] at crate level. This puts all templates to the crate's root and makes them available everywhere. Since macros with colliding names can overwrite each other, different names are a necessity. Additionally, the same rule as above applies and you should take care that templates are defined before they're used in apply calls.

#[export] Attribute

:warning: Version 0.2.0 introduce a breaking change

If you want to export your template at the root of your crate you should annotate it by #[export] attribute. Use #[export] attribute also if you need to use the template from another crate.

This was the default behaviour in the 0.1.x versions.

Example: note that we don't use #[macro_use] attribute.

mod inner {
    mod sub {
        use rstest_reuse::*;
        #[template]
        #[export]
        #[rstest(a,  b,
            case(2, 2),
            case(4/2, 2),
            )
        ]
        fn two_simple_cases(a: u32, b: u32) {}
    }
}
use rstest_reuse::*;
use rstest::*;

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

Disclamer

This crate is in a development stage. I don't know if I'll include it in rstest or change 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

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.