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insta: a snapshot testing library for Rust

Snapshots tests (also sometimes called approval tests) are tests that assert values against a reference value (the snapshot). This is similar to how assert_eq! lets you compare a value against a reference value but unlike simple string assertions, snapshot tests let you test against complex values and come with comprehensive tools to review changes.

Snapshot tests are particularly useful if your reference values are very large or change often.

#[test]
fn test_hello_world() {
    insta::assert_debug_snapshot!(vec![1, 2, 3]);
}

Curious? There is a screencast that shows the entire workflow: watch the insta introduction screencast. Or if you're not into videos, read the 5 minute introduction.

Insta also supports inline snapshots which are stored right in your source file instead of separate files. This is accomplished by the companion cargo-insta tool.

For looking at .snap files there is a vscode extension which can syntax highlight snapshot files, review snapshots and more. It can be installed from the marketplace: view on marketplace.

Insta uses similar for all its diffing operations. You can use it independently of insta. You can use the similar-asserts crate to get inline diffs for the standard assert_eq! macro to achieve insta like diffs for regular comparisons:

use similar_asserts::assert_eq;

fn main() {
    let reference = vec![1, 2, 3, 4];
    assert_eq!(reference, (0..4).collect::<Vec<_>>());
}

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