Pact Contract Testing

Pact is a consumer-driven contract testing tool that ensures different services (e.g., a frontend and an API) can communicate correctly.

Tutorial

Ready to get started? Check out our Step-by-Step Contract Testing Tutorial.

Why Contract Testing?

In a microservices architecture, traditional E2E tests are often slow, flaky, and hard to maintain. Contract testing allows you to:

• Decouple Teams: Develop and test services independently.
• Fast Feedback: Catch breaking API changes at build time.
• Reduce Flakiness: Replace unstable E2E tests with fast, deterministic contract tests.

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🛠 Configuration

Enable Pact in your .env file:

# Enable Pact
PACT_ENABLED=true

# Consumer & Provider Names
PACT_CONSUMER=my-web-app
PACT_PROVIDER=my-api-service

# Pact Broker (Optional)
PACT_BROKER_URL=https://your-pact-broker.com
PACT_BROKER_TOKEN=your-token

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🧑‍💻 Consumer Testing Tutorial

Consumer tests define the expectations for how the provider should behave.

1. Create a Consumer Test

Create a file in tests/contract/consumer/user.spec.js:

import { pactManager } from '../../../src/core/contracts/pact.manager.js';
import axios from 'axios';

describe('User API Contract', () => {
  const pact = pactManager.setup();

  it('should return user details', async () => {
    // 1. Define Interaction
    await pactManager.addInteraction({
      state: 'user with ID 1 exists',
      uponReceiving: 'a request for user 1',
      withRequest: {
        method: 'GET',
        path: '/users/1',
      },
      willRespondWith: {
        status: 200,
        body: {
          id: 1,
          name: 'John Doe',
        },
      },
    });

    // 2. Execute Test against the Mock Server
    await pactManager.executeTest(async (mockServer) => {
      const response = await axios.get(`${mockServer.url}/users/1`);
      expect(response.status).toBe(200);
      expect(response.data.name).toBe('John Doe');
    });
  });
});

2. Generate the Pact File

Run the tests to generate the JSON contract in the /pacts directory.

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🏗 Provider Verification

Provider verification ensures that the real API service actually respects the contracts defined by the consumers.

1. Verification Script

Create a script (e.g., pact-verify.js) that uses the Pact Verifier:

import { Verifier } from '@pact-foundation/pact';

const opts = {
  provider: 'my-api-service',
  providerBaseUrl: 'http://localhost:3000',
  pactBrokerUrl: process.env.PACT_BROKER_URL,
  pactBrokerToken: process.env.PACT_BROKER_TOKEN,
  publishVerificationResult: true,
  providerVersion: '1.0.0',
};

new Verifier(opts).verifyProvider();

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🚀 CLI Commands

To keep contract tests isolated, use the following recommended scripts in package.json:

Command	Description
npm run test:contract	Run consumer-side contract tests.
npm run pact:publish	Publish generated pacts to the Broker.
npm run pact:verify	Run provider-side verification.