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Micro Frontends Architecture with Module Federation · Lesson

Contract Testing Between Micro Frontends

Learn how contract testing verifies that the interfaces micro frontends expose and consume stay compatible, catching breaking changes before deployment.

Contract Testing Between Micro Frontends is a free Micro Frontends Architecture with Module Federation lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Micro Frontends Architecture with Module Federation learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

The Integration Gap

Unit tests check one MFE in isolation; E2E tests are slow and brittle. Contract testing fills the gap by verifying the agreements between MFEs without running everything together.

What Is a Contract?

A contract is the shape of an interaction between two parties — the exposed module signature, an event payload, or a shared state shape. Both sides must agree on it.

Consumer-Driven Contracts

In consumer-driven contract testing, the consumer defines what it expects from a provider. The provider then verifies it actually meets those expectations.

Contracts in Federation

For micro frontends, contracts commonly cover:

  • Exposed module props/signatures
  • Custom event names and payloads
  • Shared state structure
  • Shared API response shapes

A Props Contract Example

If a remote exposes a Widget, the consumer expects specific props. The contract records those expectations explicitly.

// consumer expects:
// <Widget productId: number, onAdd: function />

Writing a Consumer Expectation

The consumer writes a test describing the interface it relies on, generating a contract artifact the provider can check against.

expectInterface("cart/Widget", {
  props: { productId: "number", onAdd: "function" }
});

Verifying on the Provider Side

The provider runs a verification test confirming its exposed module still satisfies every consumer contract before it deploys.

verifyContracts("cart/Widget"); // fails if props changed

Event Contract Testing

For event-based communication, the contract pins the event name and payload schema, so renaming an event or dropping a field is caught immediately.

{ event: "cart:add", detail: { productId: "number" } }

Where Contracts Live

Store contracts in a shared location (a broker or repo) both teams can access. Tools like Pact provide a broker; a shared schema package is a simpler alternative.

Fitting into CI

Run provider contract verification in CI on every change. A broken contract fails the build before the incompatible MFE can reach production.

Benefits of Contract Testing

Contract tests give you:

  • Fast feedback without full integration
  • Confidence to deploy independently
  • Early detection of breaking interface changes
  • Clear, documented interfaces between teams

Quick Check

Test your contract-testing knowledge.

Recap

You learned contract testing for MFEs:

  • Contracts capture agreements on props, events, and state
  • Consumers define expectations; providers verify them
  • Store contracts in a broker or shared schema
  • Run verification in CI to block breaking changes
  • Enables confident independent deployment

Contract tests are the fast middle layer of the MFE testing pyramid.

Frequently asked questions

Is the “Contract Testing Between Micro Frontends” lesson free?

Yes — the full text of “Contract Testing Between Micro Frontends” is free to read here on the web, and the Micro Frontends Architecture with Module Federation course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Micro Frontends Architecture with Module Federation course, upgrade to CoddyKit PRO.

What will I learn in “Contract Testing Between Micro Frontends”?

Learn how contract testing verifies that the interfaces micro frontends expose and consume stay compatible, catching breaking changes before deployment. You practise Micro Frontends Architecture with Module Federation with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Micro Frontends Architecture with Module Federation?

No prior experience is required. Micro Frontends Architecture with Module Federation on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Contract Testing Between Micro Frontends” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Micro Frontends Architecture with Module Federation lesson?

Yes. Every Micro Frontends Architecture with Module Federation lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Unit Testing Federated Components
  2. Integration Testing Strategies
  3. End-to-End Testing Across Apps
  4. Contract Testing Between Micro Frontends
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