Generated tests for trait impls

Issue by Kimundi
Monday Feb 04, 2013 at 12:53 GMT

For earlier discussion, see https://github.com/rust-lang/rust/issues/4782

This issue was labelled with: A-an-interesting-project, A-testsuite, A-traits, I-wishlist in the Rust repository

After an discussion about how for example 0 == -0, and how it interacts with traits, I had the thought it might be nice to have unit tests on traits that get generated for for each impl of it.
Example:

trait Bar {
    static fn zero() -> Self;
    fn neg(&self) -> Self;
}

#[test(trait)]
fn test_bar<T: Bar>() {
    let x: T = Bar::zero();
    let y = x.neg();
    assert x == y;
}

in some other crate:

impl Bar for float {
    static fn zero() -> float { 0.0 }
    fn neg(&self) -> float { - *self }
}

Then a rustc --test for that crate would generate this function:

#[test]
fn test_bar_float() { test_bar::<float>() }

This would require trait test to somehow be made publicly callable from other crates for test compilation.

Alternative example, which might be easier to implement:

trait Bar {
    static fn zero() -> Self;
    fn neg(&self) -> Self;

    #[test]
    fn test_bar() {
        let x: Self = zero();
        let y = x.neg();
        assert x == y;
    }
}

Begin with the earlier discussion in issue 4782 and the trait-test examples in this issue. A complete result would establish an agreed design and implement generated tests for each trait impl or trait-defined tests, including cross-crate test compilation; no source files or existing tests are identified here.