Hello Snapshot Testing

Snapshots tests (also sometimes called approval tests) are tests that assert values against a reference value (the snapshot). Think of it as a supercharged version of assert_eq!. It lets you compare a value against a reference value but unlike simple assertions the reference value is managed by insta for you.

What's in the Box?

• Interactive snapshot reviews: with cargo-insta you can perform reviews of all changed snapshots conveniently.
• Inline snapshots: insta can store snapshots right within your source file.
• External snapshots: it's also possible to store snapshots as separate files.
• Redactions: if you have output which can change between test runs (such as random identifiers, timestamps or others) you can instruct insta to redact these parts.
• Flexible formats: you can pick between snapshoting into different formats such as JSON, YAML, TOML, CSV or others.
• Editor Support: insta also provides a VS Code Extension that lets you review snapshots right from within your editor.
• Pretty Diffs: insta renders beautiful snapshot diffs right in your terminal with the help of the similar crate.
• Supports older Rust: insta, similar and similar-asserts support Rust down to 1.51.
• Apache-2.0 licensed: because the best tools are Open Source under a convenient license.

What Does This Look Like?

Pretty simple. You write a test function where you perform some sort of computation and then use one of the insta provided assertion macros:

#[test]
fn test_simple() {
    insta::assert_yaml_snapshot!(calculate_value());
}

Note that no reference value is provided. Instead the reference value is placed on the first test run in a separate snapshot file. Insta will automatically manage that snapshot for you.

Test Workflow

This is what this process looks like in an actual example:

Learn More

Want to learn more?

• There is a 12 minute introduction screencast that walks you through how it works: Snapshot Testing with Insta
• Read the quickstart for more information
• Read the API documentation for a deep dive on the API