#federation

• Type: boolean
• Default: false
• CLI: --federation

Whether to enable Module Federation compatibility mode.

This option applies to Rstest's Node-based runner, including testEnvironment: 'node' and DOM-simulated environments such as jsdom and happy-dom. It does not enable or change Rstest Browser Mode (browser.enabled: true).

Rstest evaluates test bundles inside a single worker runtime so that module mocks stay effective. Module Federation runtimes load remote entries and chunks on their own — via Node fs/vm/eval or over HTTP — outside of that runtime. When federation is enabled, Rstest installs additional runtime shims to make the two work together:

• Externalized dynamic imports get a globalThis fallback, so federation runtime chunks evaluated via vm/eval can still load modules with Node's native dynamic import.
• Module Federation's placeholder chunk handlers (consumes / remotes) are kept from throwing before the federation runtime initializes.
• Federation runtime plugins cannot replace Rstest's chunk-loading handlers, which would otherwise evaluate chunks outside the test runtime and lose mocks.
• Node-targeted federation runs use Rstest's CommonJS worker loader and can serve virtual async-node chunks from the in-memory build output.

npx rstest --federation

import { defineConfig } from '@rstest/core';

export default defineConfig({
  federation: true,
});

#Testing a federated app

federation only prepares the test runtime. The Module Federation build itself (remotes, exposes, shared modules) is configured through a bundler plugin such as @module-federation/rstest, which applies the federation setup to the Rstest build:

import { federation } from '@module-federation/rstest';
import { defineConfig } from '@rstest/core';

export default defineConfig({
  federation: true,
  plugins: [
    federation({
      name: 'main_app',
      remotes: {
        'component-app': 'component_app@http://localhost:3001/remoteEntry.js',
      },
      shared: {
        react: { singleton: true },
      },
    }),
  ],
});

See the federation example for a complete setup with HTTP remotes, local CommonJS remotes, and SSR tests.