How to Use Snapshot Testing in Rust (insta crate)

Add the insta crate to your dependencies, import it, and wrap your test assertions with insta::assert_snapshot! to automatically generate and compare output snapshots.

use insta::assert_snapshot;

#[test]
fn test_output() {
    let output = "Hello, Rust!";
    assert_snapshot!(output);
}

Run cargo insta test to execute tests and review new snapshots, then cargo insta review to accept or reject changes.

Snapshot testing saves the expected output of your code as a reference file. When you run tests again, the tool compares the current output to that saved file to catch unintended changes. It is like taking a photo of your code's result and checking if the next photo looks exactly the same.