[][src]Crate insta

insta: a snapshot testing library for Rust

How it Operates

This crate exports three basic macros for snapshot testing: assert_snapshot_matches! for comparing basic string snapshots, assert_debug_snapshot_matches! for snapshotting the debug print output of a type and the assert_serialized_snapshot_matches! macro becomes available which serializes an object with serde to yaml before snapshotting.

Snapshots are stored in the snapshots folder right next to the test file where this is used. The name of the file is <module>__<name>.snap where the name of the snapshot has to be provided to the assertion macro.


Install insta and cargo-insta:

This example is not tested
$ cargo add --dev insta
$ cargo install cargo-insta
This example is not tested
use insta::assert_debug_snapshot_matches;

fn test_snapshots() {
    let value = vec![1, 2, 3];
    assert_debug_snapshot_matches!("snapshot_name", value);

The recommended flow is to run the tests once, have them fail and check if the result is okay. By default the new snapshots are stored next to the old ones with the extra .new extension. Once you are satisifed move the new files over. You can also use cargo insta review which will let you interactively review them:

This example is not tested
$ cargo test
$ cargo insta review

For more information on updating see Snapshot Updating.

Snapshot files

The committed snapshot files will have a header with some meta information that can make debugging easier and the snapshot:

This example is not tested
created: "2019-01-21T22:03:13.792906+00:00"
creator: insta@0.3.0
expression: "&User{id: Uuid::new_v4(), username: \"john_doe\".to_string(),}"
source: tests/test_redaction.rs

Snapshot Updating

During test runs snapshots will be updated according to the INSTA_UPDATE environment variable. The default is auto which will write all new snapshots into .snap.new files if no CI is detected.


  • auto: the default. no for CI environments or new otherwise
  • always: overwrites old snapshot files with new ones unasked
  • new: write new snapshots into .snap.new files.
  • no: does not update snapshot files at all (just runs tests)

When new is used as mode the cargo-insta command can be used to review the snapshots conveniently:

This example is not tested
$ cargo install cargo-insta
$ cargo test
$ cargo insta review

"enter" or "a" accepts a new snapshot, "escape" or "r" rejects, "space" or "s" skips the snapshot for now.

For more information invoke cargo insta --help.

Test Assertions

By default the tests will fail when the snapshot assertion fails. However if a test produces more than one snapshot it can be useful to force a test to pass so that all new snapshots are created in one go.

This can be enabled by setting INSTA_FORCE_PASS to 1:

This example is not tested
$ INSTA_FORCE_PASS=1 cargo test --no-fail-fast



Assets a Debug snapshot.


Assets a Serialize snapshot.


Assets a string snapshot.



A helper to work with stored snapshots.