Integration Testing

Understanding integration testing helps you work with single-spa confidently. Here you will learn the core ideas behind integration testing, see working code, and pick up best practices used on real teams.

Integration Testing Overview

Integration Testing lets you structure single-spa work so it stays readable, testable, and easy to scale. Instead of ad-hoc code, you follow a clear pattern that other developers can recognise immediately.

The key is to keep integration testing focused and predictable. Start from the minimal example here, then layer in only the complexity your feature actually needs.

import * as app from './org-checkout.js';

test('exports single-spa lifecycles', () => {
  expect(typeof app.bootstrap).toBe('function');
  expect(typeof app.mount).toBe('function');
  expect(typeof app.unmount).toBe('function');
});

Verify each micro frontend exports valid single-spa lifecycle functions.

Integration Testing Example

registerApplication({
  name: '@org/app',
  app: () => System.import('@org/app'),
  activeWhen: ['/app'],
});
start();

Start from a minimal Integration Testing example and grow it only as needed.
Keep configuration explicit so Integration Testing behaves the same in every environment.
Name things clearly so teammates understand your Integration Testing at a glance.
Add tests around Integration Testing early to lock in expected behaviour.

Single-SPA Cheatsheet

Core single-spa APIs related to integration testing.

API	Example	Purpose
registerApplication	`registerApplication({ name, app, activeWhen })`	Register a micro frontend
activeWhen	`activeWhen: ['/checkout']`	Route ownership
start	`start()`	Begin routing
bootstrap	`export async function bootstrap()`	One-time setup
mount	`export async function mount(props)`	Render the app
unmount	`export async function unmount(props)`	Clean up the app
import map	`systemjs-importmap`	Locate app bundles

How Integration Testing Works in Single-SPA

Integration Testing is part of how single-spa lets multiple applications — even in different frameworks — coexist on one page. A root config registers each app and controls when it is active.

Verify each micro frontend exports valid single-spa lifecycle functions.

A root config registers apps and calls start().
Each app exports bootstrap, mount, and unmount lifecycles.
activeWhen decides which routes each app owns.
Import maps resolve each app's bundle at runtime.

Practical Guidance for Integration Testing

For reliable micro frontends, integration testing should isolate failures and keep shared state minimal. Let each team own its app end to end while agreeing on a few shared contracts.

Concern	Recommendation
Isolation	One app's crash should not break others
Shared state	Prefer shared utility modules over globals
Routing	Keep activeWhen rules explicit and non-overlapping
Deployment	Release via import-map updates per app

Common Mistakes

Skipping error handling and edge cases when wiring up integration testing.
Leaving integration testing untested, so regressions slip into production.
Over-engineering integration testing before you actually need the extra flexibility.
Ignoring documentation, which makes integration testing hard for the next developer to change.

Key Takeaways

Integration Testing is a core part of working effectively with single-spa.
Start small and keep integration testing focused on a single responsibility.
Apply consistent patterns so integration testing scales across your project.
Test and document integration testing to keep it maintainable over time.

Pro Tip

When you get stuck on integration testing, reduce it to the smallest reproducible example first — most single-spa issues become obvious once the noise is gone.