Jest Snapshot Serializer to Remove ANSI Escape Codes

Problem

When you create your own custom jest matchers, you'll want to test that those matchers produce the expected output strings when errors occur. Jest snapshots are a great way to do that. The problem is, jest error output contains extra characters that add little value to your jest matcher tests and make the snapshot text difficult to read and review.

One example is extra quotes and quote escape characters (\) which can be quite deeply nested in some error output strings. You can use the jest-snapshot-serializer-raw package to help with these.

A second problem is ANSI escape codes which apply color and formatting. There is a jest-snapshot-serializer-ansi package to remove these codes, but it currently has dependencies that are flagged as moderate vulnerabilities.

Solution

@relmify/jest-serializer-strip-ansi removes ANSI escape codes from Jest snapshot captures, and does so with no runtime dependencies.

Installation

With npm:

npm install -D @relmify/jest-serializer-strip-ansi

With yarn:

yarn add -D @relmify/jest-serializer-strip-ansi

Setup and Use

To use this snapshot serializer for all jest snapshots, add @relmify/jest-serializer-strip-ansi/always to your jest configuration.

Setup with package.json

In your package.json file add:

"jest": {
  "snapshotSerializers": ["@relmify/jest-serializer-strip-ansi/always"]
}

Or if you are also using jest-snapshot-serializer-raw:

"jest": {
  "snapshotSerializers": ["@relmify/jest-serializer-strip-ansi/always", "jest-snapshot-serializer-raw/always"]
}

Setup with jest.config.js

// jest.config.js
module.exports = {
  snapshotSerializers: ['@relmify/jest-serializer-strip-ansi/always'],
};

Or if you are also using jest-snapshot-serializer-raw:

// jest.config.js
module.exports = {
  snapshotSerializers: ['@relmify/jest-serializer-strip-ansi/always', 'jest-snapshot-serializer-raw/always'],
};

Per-file use

If you want to use the serializer only in certain test files, then instead of adding the serializer to your jest configuration, you can add the following to your selected test files:

import { stripAnsi } from '@relmify/jest-serializer-strip-ansi';

expect.addSnapshotSerializer(stripAnsi);

Note that you can add multiple snapshot serializers in your jest configuration, but you can only add one snapshot serializer at a time using expect.addSnapshotSerializer(). Calling expect.addSnapshotSerializer() a second time will replace the previously added serializer.

LICENSE

MIT