Patterns

This is a collection of common patterns for how to best use Insta in some more complex setups.

rstest

If you are using the rstest crate, more specifically the #[case] feature you might want to use this pattern to ensure a pleasant experience. Because rstest will parametrize your tests insta will normally have challenges associating your snapshots with the right parametrized test. In that situation you can use the following macro to add a suffix to your snapshot tests specific to your input values:

macro_rules! set_snapshot_suffix {
    ($($expr:expr),*) => {
        let mut settings = insta::Settings::clone_current();
        settings.set_snapshot_suffix(format!($($expr,)*));
        let _guard = settings.bind_to_scope();
    }
}

After that you can trivially set the snapshot suffix in your parametrized test:

#[rstest]
#[case(0, 2)]
#[case(2, 4)]
fn test_it(#[case] a: usize, #[case] b: usize) {
    set_snapshot_suffix!("{}-{}", a, b);
    insta::assert_debug_snapshot!(a * b);
}

In the above example the snapshots will then be named as follows:

tests/snapshots/example__it@0-2.snap
tests/snapshots/example__it@2-4.snap