test-case 1.2.3

Provides #[test_case(...)] procedural macro attribute for generating parametrized test cases easily

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Test Case


This crate provides #[test_case] procedural macro attribute that generates multiple parametrized tests using one body with different input parameters. A test is generated for each data set passed in test_case attribute. Under the hood, all test cases that share same body are grouped into mod, giving clear and readable test results.

Getting Started

First of all you have to add this dependency to your Cargo.toml:

test-case = "1.2.3"

Additionally, you have to import the procedural macro with use statement:

use test_case::test_case;

Example usage:

// The next two lines are not needed for 2018 edition or newer
extern crate test_case;

mod tests {
    use test_case::test_case;

    // Not needed for this example, but useful in general
    use super::*;

    #[test_case(4,  2  ; "when operands are swapped")]
    #[test_case(-2, -4 ; "when both operands are negative")]
    #[test_case(2,  4  ; "when both operands are positive")]
    fn multiplication_tests(x: i8, y: i8) {
        let actual = (x * y).abs();

        assert_eq!(8, actual)

    // You can still use regular tests too
    fn addition_test() {
        let actual = -2 + 8;
        assert_eq!(6, actual)

Output from cargo test for this example:

$ cargo test

running 4 tests
test tests::addition_test ... ok
test tests::multiplication_tests::when_both_operands_are_negative ... ok
test tests::multiplication_tests::when_both_operands_are_positive ... ok
test tests::multiplication_tests::when_operands_are_swapped ... ok

test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out


If your only assertion is just assert_eq!, you can pass the expectation as macro attribute using => syntax:

#[test_case( 2 => 2 ; "returns given number for positive input")]
#[test_case(-2 => 2 ; "returns opposite number for non-positive input")]
#[test_case( 0 => 0 ; "returns 0 for 0")]
fn abs_tests(x: i8) -> i8 {
   if x > 0 { x } else { -x }

Which is equivalent to

#[test_case( 2, 2 ; "returns given number for positive input")]
#[test_case(-2, 2 ; "returns opposite number for non-positive input")]
#[test_case( 0, 0 ; "returns 0 for 0")]
fn abs_tests(x: i8, expected: i8){
   let actual = if x > 0 { x } else { -x };

   assert_eq!(expected, actual);

Attributes and expectation may be any expresion unless they contain =>, e.g.

#[test_case(None,        None    => 0 ; "treats none as 0")]
#[test_case(Some(2),     Some(3) => 5)]
#[test_case(Some(2 + 3), Some(4) => 2 + 3 + 4)]
fn fancy_addition(x: Option<i8>, y: Option<i8>) -> i8 {
    x.unwrap_or(0) + y.unwrap_or(0)

Note: in fact, => is not prohibited, but the parser will always treat last => sign as beginning of expectation definition.

Test case names are optional. They are set using ; followed by string literal at the end of macro attributes.

Example generated code:

mod fancy_addition {
    use super::*;

    fn fancy_addition(x: Option<i8>, y: Option<i8>) -> i8 {
        x.unwrap_or(0) + y.unwrap_or(0)

    fn treats_none_as_0() {
        let expected = 0;
        let actual = fancy_addition(None, None);

        assert_eq!(expected, actual);

    fn some_2_some_3() {
        let expected = 5;
        let actual = fancy_addition(Some(2), Some(3));

        assert_eq!(expected, actual);

    fn some_2_3_some_4() {
        let expected = 2 + 3 + 4;
        let actual = fancy_addition(Some(2 + 3), Some(4));

        assert_eq!(expected, actual);



Context ignored test cases (deprecated, will be dropped in 2.0.0)

If test case name (passed using ; syntax described above) contains a word "inconclusive", generated test will be marked with #[ignore].

Keyword 'inconclusive'

If test expectation is preceded by keyword inconclusive the test will be ignored as if it's description would contain word inconclusive

#[test_case("XX" ; "inconclusive - parsing letters temporarily doesn't work, but it's ok")]
#[test_case("na" => inconclusive ())]
fn parses_input(input: &str) {
    // ...

Generated code:

mod parses_input {
    // ...

    pub fn _42() {
        // ...

    pub fn inconclusive_parsing_letters_temporarily_doesn_t_work_but_it_s_ok() {
        // ...


If test expectation is preceded by matches keyword, the result will be tested whether it fits within provided pattern.

#[test_case("foo", "bar" => matches ("foo", _) ; "first element of zipped tuple is correct")]
#[test_case("foo", "bar" => matches (_, "bar") ; "second element of zipped tuple is correct")]
fn zip_test<'a>(left: &'a str, right: &'a str) -> (&'a str, &'a str) {
    (left, right)


If test case expectation is preceded by panics keyword and the expectation itself is &str or expresion that evaluates to &str then test case will be expected to panic during execution.

#[test_case("foo" => panics "invalid input")]
fn test_panicking(input: &str) {
    if input == "foo" {
        panic!("invalid input")

is|it (feature = "hamcrest_assertions")

This feature requires addition of hamcrest2 crate to your Cargo.toml:

test-case = { version = "1.1.0", features = ["hamcrest_assertions"] }
hamcrest2 = "0.3.0"

After that you can use test cases with new keywords is and it which will allow you to use hamcrest2 assertions (doc)

#[test_case(&[1, 3] => is empty())]
#[test_case(&[2, 3] => it contains(2))]
#[test_case(&[2, 3] => it not(contains(3)))]
#[test_case(&[2, 4] => it contains(vec!(2, 4)))]
#[test_case(&[2, 3] => is len(1))]
fn removes_odd_numbers(collection: &[u8]) -> &Vec<u8> {
    Box::leak(Box::new(collection.into_iter().filter(|x| *x % 2 == 0).copied().collect()))

async in test cases

Test cases can work with tokio, async-std and other runtimes, provided #[test...] attribute from mentioned libraries is used as a last attribute.


#[test_case("Hello, world" => true)]
async fn runs_async_task(input: &str) -> bool {

Porting from Rust #[test]s with Result types

It is important to note that test-case does not support the Rust 2018+ idiom of failing tests by returning a Result<T, E> with an error type. The simplest way to remedy this is to append ... => Ok(_) to each #[test-case(...) expression, e.g:

#[test_case( 0 => Ok(_) ; "Test with 0")]

Previously, tests relying on the return error being checked would silently pass; as of 1.2.2 attempting to return a Result<> without an appropriate return check in the expression will result in a compilation error. However if you wish to keep the old behaviour for some reason the feature flag allow_result will disable the check.


Licensed under of MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)


All contributions and comments are more than welcome! Don't be afraid to open an issue or PR whenever you find a bug or have an idea to improve this crate.

Recommended tools:

  • cargo readme - to regenerate README.md based on template and lib.rs comments
  • cargo insta - to review test snapshots
  • cargo edit - to add/remove dependencies
  • cargo fmt - to format code
  • cargo clippy - for all insights and tips
  • cargo fix - for fixing warnings