Crate assert2ify[][src]

Expand description

This crates offers the #[assert2ify] attribute, a one-line solution to replace standard library assertions in your code with the more expressive assertions from the assert2 crate.

The attribute not only replaces simple assertions such as assert!(...) or assert_eq!(...) but also more complicated constructs like assert!(matches!(...)) with assertions with way better error messages.


Rust’s built-in support for tests and assertions is great in so many ways, but the standard library assertions are lacking in terms of error messages. This is where the assert2 crate comes in handy because it offers assertions with very helpful error messages.

Let’s say we have some assertion on the length of a vector, such as assert!(my_vector.len() < 5). If this assertion panics, it will just tell you that the condition was violated, but it will not tell you what the actual length of the vector was. To know that, you would have to debug the test or add extra logging output. The assert2 crate comes to the rescue, because if we had written the assertion as assert2::assert!(my_vector.len() < 5) then a possible failure would look like this (plus some nice colors):

Assertion failed at tests/
  assert!( my_vector.len() < 5 )
with expansion:
  7 < 5

You can annotate any function (usually a test case) with #[assert2ify] and it takes care of replacing the assertions inside the functions.


Just annotate any function with the #[assert2ify] attribute and have the attribute replace the assertions in your code with the assertions of the assert2 crate. It does not only replace simple assertions, but also more complicated constructs like assert!(matches!(...)) with something much more helpful. The assertions work as they did before, but they offer way better error messages.

Furthermore, the attribute allows you to replace assertions with checks, which do not fail right away but only once the test case is completely finished. This can help if you want to catch every assertion that fails in a test in a single pass. Just use the attribute as #[assert2ify(check)] for this.

See what more the assert2ify attribute can do for you in the documentation. The docs also go into detail about the limitations of the attribute.

Attribute Macros


Annotate your functions (usually test cases) with this attribute and have it replace the assertions the function with the more powerful assertions from the assert2 crate.