#test #tests #testing

macro static_test

Attribute macro for writing tests which check that a given condition ALWAYS holds true or that a given code path is ALWAYS unreachable

1 unstable release

0.1.0 Oct 20, 2019

#581 in Testing


194 lines

Build Status




use static_test::static_test;

fn test_slice_get_will_always_succeed_if_length_is_known( buffer: &[u8] ) -> u8 {
    assume!( buffer.len() == 1 );
    match buffer.get( 0 ) {
        Some( &value ) => value,
        None => static_unreachable!()

fn test_multiplication( value: u8 ) {
    assume!( value == 2 );
    static_assert!( value * 10 == 20 );

You can specify arbitrary types as parameters and as the return type of every function you mark as #[static_test]. The bodies of those functions will never actually be executed, however every static_assert! and static_unreachable! will still be indirectly checked.

If the compiler can't prove that every static_assert! will always hold true and that every static_unreachable! will always be unreachable then an error will be generated at link time.

Every function marked as #[static_test] will be turned into a #[test] function.

The assume!, static_assert! and static_unreachable! macros are defined by the procedural macro and are only available inside functions marked as #[static_test].


  • This requires at least Rust 1.40.
  • This requires the linker to run, so it will have no effect on cargo check.
  • This will only work when you compile your code with optimizations turned on, as it depends on the optimizer to remove unreachable static_assert!s and static_unreachable!s.
  • If an assertion fails the error message will not be great.


This is inspired by the no_panic crate.


Licensed under either of

at your option.


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


~30K SLoC