Test Case

Overview

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:

[dev-dependencies]
test-case = "0.3.2"

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

use test_case::test_case;

The crate depends on proc_macro feature that has been stabilized on rustc 1.29+.

Example usage:

#![cfg(test)]
extern crate test_case;

use test_case::test_case;

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

    assert_eq!(8, actual)
}

Output from cargo test for this example:

$ cargo test

running 3 tests
test multiplication_tests::when_both_operands_are_possitive ... ok
test multiplication_tests::when_both_operands_are_negative ... ok
test multiplication_tests::when_operands_are_swapped ... ok

test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

Examples

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 {
    #[allow(unused_imports)]
    use super::*;

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

    #[test]
    fn treats_none_as_0() {
        let expected = 0;
        let actual = fancy_addition(None, None);

        assert_eq!(expected, actual);
    }

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

        assert_eq!(expected, actual);
    }

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

        assert_eq!(expected, actual);
    }
}

Inconclusive (ignored) test cases (since 0.2.0)

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

#[test_case("42")]
#[test_case("XX" ; "inconclusive - parsing letters temporarily doesn't work but it's ok")]
fn parses_input(input: &str) {
    // ...
}

Generated code:

mod parses_input {
    // ...

    #[test]
    pub fn _42() {
        // ...
    }

    #[test]
    #[ignore]
    pub fn inconclusive_parsing_letters_temporarily_doesn_t_work_but_it_s_ok() {
        // ...
    }

Note: word inconclusive is only reserved in test name given after ;.

License

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

Contribution

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