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= snap :toc:

Clojure(Script) library for snapshot testing

== Usage

[source,clojure]

{:deps {juxt/snap {:git/url "https://github.com/juxt/snap" :sha "..."}}}

[source,clojure]

(deftest react-test (snap.core/match-snapshot ::Root (js->clj (RootComponent.toJSON))))

The first time the test is run it creates a snapshot of the test value. After a snapshot is created every successive run compares the supplied value against the snapshot. If a test failure is found you can either:

• Fix the code that created the unintended change
• Ensure this is an intended change, delete the old snapshot and let snap create a new one

Make sure you commit the snapshots to source code!

== What is snapshot testing

Snapshot tests are a very useful tool whenever you want to make sure your UI does not change unexpectedly.

A typical snapshot test case for a mobile app renders a UI component, takes a screenshot, then compares it to a reference image stored alongside the test. The test will fail if the two images do not match: either the change is unexpected, or the screenshot needs to be updated to the new version of the UI component.

This library is inspired by Jest snapshot https://facebook.github.io/jest/docs/en/snapshot-testing.html[testing] The idea seems so good to me that it can be applied to other cases beyond UI tests.

== Examples

Check the /example directory for a React tree test and a Datomic query test

== Todo

• [x] ClojureScript support
• [x] Add Datascript example
• [x] Add configurable options (snapshot path, pprint)