Diffing snapshot utility for Jest
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.
yarn add --dev snapshot-diff
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(); });
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
exports[snapshot difference between 2 React components state 1
] = `
"-
@@ -27,11 +27,11 @@
By default,
snapshot-diffuses a built in React serializer based on
react-test-renderer. The serializers used can be set by calling
setSerializerswith 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.
setSerializerscan 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!
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 ]);
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 ]);
By default Jest adds extra quotes around strings so it makes diff snapshots of objects too noisy. To fix this –
snapshot-diffcomes with custom serializer, which you can add directly in your tests or in
setupFilesscript:
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'), ], };
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
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!