snapshot-diff


Diffing snapshot utility for Jest. Takes two values, and return their difference as a string, ready to be snapshotted with toMatchSnapshot().
Especially helpful when testing the difference between different React component states.

Installation

``bash
yarn add --dev snapshot-diff
`

Usage

#### With default jest matcher

`js
const snapshotDiff = require('snapshot-diff');

test('snapshot difference between 2 strings', () => {
expect(snapshotDiff(a, b)).toMatchSnapshot();
});

const React = require('react');
const Component = require('./Component');

test('snapshot difference between 2 React components state', () => {
expect(
snapshotDiff(, )
).toMatchSnapshot();
});
`

#### With custom matcher

`js
const { toMatchDiffSnapshot } = require('snapshot-diff');

expect.extend({ toMatchDiffSnapshot });

test('snapshot difference between 2 strings', () => {
expect(a).toMatchDiffSnapshot(b);
});

const React = require('react');
const Component = require('./Component');

test('snapshot difference between 2 React components state', () => {
expect().toMatchDiffSnapshot(

);
});
`

... alternatively import it once, for instance in your tests setup file:

`js
require('snapshot-diff/extend-expect');
`

Produced snapshot:

`diff
exports[snapshot difference between 2 strings 1] =
"- First value
+ Second value

- abcx
+ abcy
"
;

exports[snapshot difference between 2 React components state 1] =
"-
+

@@ -27,11 +27,11 @@





- say
+ my name




"
;
`

Custom serializers

By default, snapshot-diff uses a built in React serializer based on react-test-renderer. The
serializers used can be set by calling
setSerializers with an array of serializers to use. The order of serializers in this array may be important to you as
serializers are tested in order until a match is found.

setSerializers can be used to add new serializers for unsupported data types, or to set a different serializer
for React components. If you want to keep the default React serializer in place, don't forget to add the default
serializers to your list of serializers!

$3

`js
const snapshotDiff = require('snapshot-diff');
const myCustomSerializer = require('./my-custom-serializer');

snapshotDiff.setSerializers([
...snapshotDiff.defaultSerializers, // use default React serializer - add this if you want to serialise React components!
myCustomSerializer
]);
`

$3

You can replace the default React serializer by omitting it from the serializer list. The following uses enzymes to-json
serializer instead:

`js
const snapshotDiff = require('snapshot-diff');
const enzymeToJson = require('enzyme-to-json/serializer');
const myCustomSerializer = require('./my-custom-serializer');

snapshotDiff.setSerializers([
enzymeToJson, // using enzymes serializer instead
myCustomSerializer
]);
`

Snapshot serializer

By default Jest adds extra quotes around strings so it makes diff snapshots of objects too noisy.
To fix this – snapshot-diff comes with custom serializer, which you can add directly in your tests or in setupFiles script:

`js
const snapshotDiff = require('snapshot-diff');

expect.addSnapshotSerializer(snapshotDiff.getSnapshotDiffSerializer());

test('snapshot difference between 2 objects', () => {
expect(snapshotDiff({ foo: 'bar' }, { foo: 'baz' })).toMatchSnapshot();
});
`

...or add it globally to your jest config:

`js
// jest.config.js
module.exports = {
snapshotSerializers: [
require.resolve('snapshot-diff/serializer.js'),
],
};
`

API

`js
type Options = {
expand?: boolean,
colors?: boolean,
contextLines?: number
};

// default export
snapshotDiff(valueA: any, valueB: any, options?: Options) => string
// custom matcher
expect(valueA: any).toMatchDiffSnapshot(valueB: any, options?: Options, testName?: string) => void
`

$3

- expand: boolean (default: false) – expand the diff, so the whole information is preserved
- colors: boolean (default: false) – preserve color information from Jest diff
- contextLines: number (default: 5) - number of context lines to be shown at the beginning and at the end of a snapshot
- stablePatchmarks: boolean (default: false) - prevent line number patch marks from appearing in
diffs. This can be helpful when diffs are breaking only because of the patch marks. Changes @@ -1,1 +1,2 @@ to @@ --- --- @@.
- aAnnotation: string (default: 'First Value') - the annotation indicating from which serialization the - lines are
- bAnnotation: string (default: 'Second Value') - the annotation indicating from which serialization the +` lines are

---

Project is MIT-licensed. Pull Requests welcome!