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.
First of all you have to add this dependency to your Cargo.toml
:
[dev-dependencies]
test-case = "1.0.0"
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+.
// The next two lines are not needed for 2018 edition or newer
#[cfg(test)]
extern crate test_case;
#[cfg(test)]
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
#[test]
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 {
#[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);
}
}
If test case name (passed using ;
syntax described above) contains a word "inconclusive", generated test will be marked with #[ignore]
.
If test expectation is preceded by keyword inconclusive
the test will be ignored as if it's description would contain word inconclusive
#[test_case("42")]
#[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 {
// ...
#[test]
pub fn _42() {
// ...
}
#[test]
#[ignore]
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")]
#[test_case("bar")]
fn test_panicking(input: &str) {
if input == "foo" {
panic!("invalid input")
}
}
It is allowed to test whether test case panics ignoring panic message via #[test_case("foo" => panics)]
(since 1.1.0).
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()))
}
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 commentscargo insta
- to review test snapshotscargo edit
- to add/remove dependenciescargo fmt
- to format codecargo clippy
- for all insights and tipscargo fix
- for fixing warnings