snapshot-diff

Diffing snapshot utility for Jest. Takes two values, and return their difference as a string, ready to be snapshotted with

toMatchSnapshot()

Installation

yarn add --dev snapshot-diff

Usage

With default jest matcher

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

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:

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

Produced snapshot:

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

react-test-renderer

setSerializers

setSerializers

Adding a new custom serializer

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
]);

Serializing React components with a different serializer

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

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

setupFiles

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:

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

API

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

Options

• 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!