#parameterized #case #decorator


Parameterized test cases and test decorators

3 releases

0.1.2 Nov 2, 2023
0.1.1 Oct 8, 2023
0.1.0 Jun 3, 2023

#69 in Testing

Download history 16/week @ 2023-08-17 16/week @ 2023-08-24 12/week @ 2023-08-31 90/week @ 2023-09-07 89/week @ 2023-09-14 34/week @ 2023-09-21 97/week @ 2023-09-28 75/week @ 2023-10-05 78/week @ 2023-10-12 90/week @ 2023-10-19 128/week @ 2023-10-26 191/week @ 2023-11-02 171/week @ 2023-11-09 482/week @ 2023-11-16 510/week @ 2023-11-23 758/week @ 2023-11-30

1,940 downloads per month
Used in 3 crates


781 lines

Parameterized Rust Tests & Test Decorators

Build Status License: MIT OR Apache-2.0 rust 1.65+ required

Documentation: Docs.rs crate docs (main)

test-casing is a minimalistic Rust framework for generating tests for a given set of test cases and decorating them to add retries, timeouts, sequential test processing etc. In other words, the framework implements:

  • Parameterized tests of reasonably low cardinality for the standard Rust test runner
  • Fully code-based, composable and extensible test decorators.

Since a separate test wrapper is generated for each case, their number should be reasonably low (roughly speaking, no more than 20). Isolating each test case makes most sense if the cases involve some heavy lifting (spinning up a runtime, logging considerable amount of information, etc.).


Add this to your Crate.toml:

test-casing = "0.1.2"

Examples: test cases

use test_casing::{cases, test_casing, TestCases};
use std::error::Error;

#[test_casing(4, [2, 3, 5, 8])]
fn numeric_test(number: i32) {
    assert!(number < 10);

// Cases can be extracted to a constant for better readability.
const CASES: TestCases<(String, i32)> = cases! {
    [2, 3, 5, 8].map(|i| (i.to_string(), i))

#[test_casing(4, CASES)]
fn parsing_number(
    #[map(ref)] s: &str,
    // ^ specifies that argument should be borrowed from `String`
    // returned by the `CASES` iterator
    expected: i32,
) -> Result<(), Box<dyn Error>> {
    assert_eq!(s.parse::<i32>()?, expected);

Other features include the support of async tests and ignore / should_panic attributes (the latter are applied to all generated cases).

use test_casing::test_casing;

#[test_casing(4, [2, 3, 5, 8])]
// ^ test attribute should be specified below the case spec
async fn test_async(number: i32) {
    assert!(number < 10);

#[test_casing(3, ["not", "a", "number"])]
#[should_panic(expected = "ParseIntError")]
fn parsing_number_errors(s: &str) {

Examples: test decorators

use test_casing::{
    decorate, test_casing, decorators::{Retry, Sequence, Timeout},

#[decorate(Retry::times(3), Timeout::secs(3))]
fn test_with_retry_and_timeouts() {
    // Test logic

static SEQUENCE: Sequence = Sequence::new().abort_on_failure();

// Execute all test cases sequentially and abort if one of them fails.
#[test_casing(4, [2, 3, 5, 8])]
async fn test_async(number: i32) {
    assert!(number < 10);

See the crate docs for more examples of usage.

Descriptive test case names

With the help of custom test frameworks APIs and a generous spicing of hacks, the names of generated tests include the values of arguments provided to the targeted test function if the nightly crate feature is enabled. As the name implies, the feature only works on the nightly Rust.

Here's an excerpt of the output of integration tests in this crate to illustrate:

test cartesian_product::case_6 [number = 5, s = "first"] ... ok
test cartesian_product::case_9 [number = 8, s = "first"] ... ok
test number_can_be_converted_to_string::case_0 [number = 2, expected = "2"] ... ok
test number_can_be_converted_to_string::case_1 [number = 3, expected = "3"] ... ok
test number_can_be_converted_to_string::case_2 [number = 5, expected = "5"] ... ok
test number_can_be_converted_to_string_with_tuple_input::case_0 [(arg 0) = (2, "2")] ... ok
test number_can_be_converted_to_string_with_tuple_input::case_1 [(arg 0) = (3, "3")] ... ok
test number_can_be_converted_to_string_with_tuple_input::case_2 [(arg 0) = (5, "5")] ... ok
test numbers_are_large::case_0 [number = 2] ... ignored, testing that `#[ignore]` attr works
test numbers_are_large::case_1 [number = 3] ... ignored, testing that `#[ignore]` attr works
test string_conversion_fail::case_0 [bogus_str = "not a number"] - should panic ... ok
test string_conversion_fail::case_1 [bogus_str = "-"] - should panic ... ok
test string_conversion_fail::case_2 [bogus_str = ""] - should panic ... ok
test unit_test_detection_works ... ok

The arguments are a full-fledged part of test names, meaning that they can be included into test filters (like cargo test 'number = 3') etc.

Alternatives and similar tools

  • The approach from this crate can be reproduced with some amount of copy-pasting by manually feeding necessary inputs to a common parametric testing function. Optionally, these tests may be collected in a module for better structuring. The main downside of this approach is the amount of copy-pasting.
  • Alternatively, multiple test cases may be run in a single #[test] (e.g., in a loop). This is fine for the large amount of small cases (e.g., mini-fuzzing), but may have downsides such as overflowing or overlapping logs and increased test runtimes.
  • The test-case crate uses a similar approach to test case structuring, but differs in how test case inputs are specified. Subjectively, the approach used by this crate is more extensible and easier to read.
  • Property testing / quickcheck-like frameworks provide a much more exhaustive approach to parameterized testing, but they require significantly more setup effort.
  • rstest supports test casing and some test decorators (e.g., timeouts).
  • nextest is an alternative test runner that supports most of the test decorators defined by this library. It does not use a code-based decorator config and does not allow for custom decorators. Tests produced with this library can be run by cargo nextest.


Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in test-casing by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.


~19K SLoC