jest-circleci-coverage

A Jest plugin that generates coverage data for CircleCI's Smarter Testing.

Usage

This plugin uses the v8 JS engine Profiler APIs to collect coverage.

Install the plugin.

pnpm add -D @circleci/jest-circleci-coverage

The Jest test environment is a peer dependency — you need to install it yourself, matching whichever environment you plan to use. The plugin supports Jest 28, 29, and 30.

For Node-based tests:

pnpm add -D jest jest-environment-node

For browser-like tests (e.g. React Testing Library) install the JSDOM environment instead:

pnpm add -D jest jest-environment-jsdom

To pin a specific major (for example to stay on Jest 29 while a newer version exists), pass an explicit version range:

pnpm add -D jest@^29 jest-environment-node@^29

Add the custom runner and reporter to your jest.config.ts:

import {createDefaultPreset} from 'ts-jest';
import type {Config} from 'jest';

const tsJestTransformCfg = createDefaultPreset().transform;

const config: Config = {
  testEnvironment: '@circleci/jest-circleci-coverage/environment-node',
  reporters: ['default', '@circleci/jest-circleci-coverage/reporter'],
  transform: {
    ...tsJestTransformCfg,
  },
};

export default config;

For browser-like tests (e.g. React Testing Library), use the JSDOM-based environment:

import {createDefaultPreset} from 'ts-jest';
import type {Config} from 'jest';

const tsJestTransformCfg = createDefaultPreset().transform;

const config: Config = {
  testEnvironment: '@circleci/jest-circleci-coverage/environment-jsdom',
  reporters: ['default', '@circleci/jest-circleci-coverage/reporter'],
  transform: {
    ...tsJestTransformCfg,
  },
};

export default config;

Set the CIRCLECI_COVERAGE environment variable when running tests to enable test coverage.

CIRCLECI_COVERAGE=coverage.json jest

Development

Install and use current node version.

NODE_VER=$(cat ./.nvmrc)
nvm install $NODE_VER
nvm use $NODE_VER

Install dependencies with pnpm.

pnpm install

Build the plugin.

pnpm build

Run tests.

pnpm test