Writing consumer tests

This tutorial guides you through writing a consumer test from scratch. To start, the consumer tests are written using jest-pact that builds on top of pact-js. This tutorial shows you how to write a consumer test for the /discussions.json REST API endpoint, which is /:namespace_name/:project_name/-/merge_requests/:id/discussions.json, that is called in the MergeRequests#show page. For an example of a GraphQL consumer test, see spec/contracts/consumer/specs/project/pipelines/show.spec.js.

Create the skeleton

Start by creating the skeleton of a consumer test. Since this is for a request in the MergeRequests#show page, under spec/contracts/consumer/specs/project/merge_requests, create a file called show.spec.js. Then, populate it with the following function and parameters:

pactWith
PactOptions
PactFn

To learn more about how the contract test directory is structured, see the contract testing test suite folder structure.

The `pactWith` function

The Pact consumer test is defined through the pactWith function that takes PactOptions and the PactFn.

import { pactWith } from 'jest-pact';

pactWith(PactOptions, PactFn);

The `PactOptions` parameter

PactOptions with jest-pact introduces additional options that build on top of the ones provided in pact-js. In most cases, you define the consumer, provider, log, and dir options for these tests.

import { pactWith } from 'jest-pact';

pactWith(
  {
    consumer: 'MergeRequests#show',
    provider: 'GET discussions',
    log: '../logs/consumer.log',
    dir: '../contracts/project/merge_requests/show',
  },
  PactFn
);

To learn more about how to name the consumers and providers, see contract testing naming conventions.

The `PactFn` parameter

The PactFn is where your tests are defined. This is where you set up the mock provider and where you can use the standard Jest methods like Jest.describe, Jest.beforeEach, and Jest.it. For more information, see https://jestjs.io/docs/api.

import { pactWith } from 'jest-pact';

pactWith(
  {
    consumer: 'MergeRequests#show',
    provider: 'GET discussions',
    log: '../logs/consumer.log',
    dir: '../contracts/project/merge_requests/show',
  },

  (provider) => {
    describe('GET discussions', () => {
      beforeEach(() => {

      });

      it('return a successful body', async () => {

      });
    });
  },
);

Set up the mock provider

Before you run your test, set up the mock provider that handles the specified requests and returns a specified response. To do that, define the state and the expected request and response in an Interaction.

For this tutorial, define four attributes for the Interaction:

state: A description of what the prerequisite state is before the request is made.
uponReceiving: A description of what kind of request this Interaction is handling.
withRequest: Where you define the request specifications. It contains the request method, path, and any headers, body, or query.
willRespondWith: Where you define the expected response. It contains the response status, headers, and body.

After you define the Interaction, add that interaction to the mock provider by calling addInteraction.

import { pactWith } from 'jest-pact';
import { Matchers } from '@pact-foundation/pact';

pactWith(
  {
    consumer: 'MergeRequests#show',
    provider: 'GET discussions',
    log: '../logs/consumer.log',
    dir: '../contracts/project/merge_requests/show',
  },

  (provider) => {
    describe('GET discussions', () => {
      beforeEach(() => {
        const interaction = {
          state: 'a merge request with discussions exists',
          uponReceiving: 'a request for discussions',
          withRequest: {
            method: 'GET',
            path: '/gitlab-org/gitlab-qa/-/merge_requests/1/discussions.json',
            headers: {
              Accept: '*/*',
            },
          },
          willRespondWith: {
            status: 200,
            headers: {
              'Content-Type': 'application/json; charset=utf-8',
            },
            body: Matchers.eachLike({
              id: Matchers.string('fd73763cbcbf7b29eb8765d969a38f7d735e222a'),
              project_id: Matchers.integer(6954442),
              ...
              resolved: Matchers.boolean(true)
            }),
          },
        };
        provider.addInteraction(interaction);
      });

      it('return a successful body', async () => {

      });
    });
  },
);

Response body `Matchers`

Notice how we use Matchers in the body of the expected response. This allows us to be flexible enough to accept different values but still be strict enough to distinguish between valid and invalid values. We must ensure that we have a tight definition that is neither too strict nor too lax. Read more about the different types of Matchers. We are currently using the V2 matching rules.

Write the test

After the mock provider is set up, you can write the test. For this test, you make a request and expect a particular response.

First, set up the client that makes the API request. To do that, create spec/contracts/consumer/resources/api/project/merge_requests.js and add the following API request. If the endpoint is a GraphQL, then we create it under spec/contracts/consumer/resources/graphql instead.

import axios from 'axios';

export async function getDiscussions(endpoint) {
  const { url } = endpoint;

  return axios({
    method: 'GET',
    baseURL: url,
    url: '/gitlab-org/gitlab-qa/-/merge_requests/1/discussions.json',
    headers: { Accept: '*/*' },
  })
}

After that's set up, import it to the test file and call it to make the request. Then, you can make the request and define your expectations.

import { pactWith } from 'jest-pact';
import { Matchers } from '@pact-foundation/pact';

import { getDiscussions } from '../../../resources/api/project/merge_requests';

pactWith(
  {
    consumer: 'MergeRequests#show',
    provider: 'GET discussions',
    log: '../logs/consumer.log',
    dir: '../contracts/project/merge_requests/show',
  },

  (provider) => {
    describe('GET discussions', () => {
      beforeEach(() => {
        const interaction = {
          state: 'a merge request with discussions exists',
          uponReceiving: 'a request for discussions',
          withRequest: {
            method: 'GET',
            path: '/gitlab-org/gitlab-qa/-/merge_requests/1/discussions.json',
            headers: {
              Accept: '*/*',
            },
          },
          willRespondWith: {
            status: 200,
            headers: {
              'Content-Type': 'application/json; charset=utf-8',
            },
            body: Matchers.eachLike({
              id: Matchers.string('fd73763cbcbf7b29eb8765d969a38f7d735e222a'),
              project_id: Matchers.integer(6954442),
              ...
              resolved: Matchers.boolean(true)
            }),
          },
        };
      });

      it('return a successful body', async () => {
        const discussions = await getDiscussions({
          url: provider.mockService.baseUrl,
        });

        expect(discussions).toEqual(Matchers.eachLike({
          id: 'fd73763cbcbf7b29eb8765d969a38f7d735e222a',
          project_id: 6954442,
          ...
          resolved: true
        }));
      });
    });
  },
);

There we have it! The consumer test is now set up. You can now try running this test.

Improve test readability

As you may have noticed, the request and response definitions can get large. This results in the test being difficult to read, with a lot of scrolling to find what you want. You can make the test easier to read by extracting these out to a fixture.

Create a file under spec/contracts/consumer/fixtures/project/merge_requests called discussions.fixture.js where you will place the request and response definitions.

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

const body = Matchers.eachLike({
  id: Matchers.string('fd73763cbcbf7b29eb8765d969a38f7d735e222a'),
  project_id: Matchers.integer(6954442),
  ...
  resolved: Matchers.boolean(true)
});

const Discussions = {
  body: Matchers.extractPayload(body),

  success: {
    status: 200,
    headers: {
      'Content-Type': 'application/json; charset=utf-8',
    },
    body,
  },

  scenario: {
    state: 'a merge request with discussions exists',
    uponReceiving: 'a request for discussions',
  },

  request: {
    withRequest: {
      method: 'GET',
      path: '/gitlab-org/gitlab-qa/-/merge_requests/1/discussions.json',
      headers: {
        Accept: '*/*',
      },
    },
  },
};

exports.Discussions = Discussions;

With all of that moved to the fixture, you can simplify the test to the following:

import { pactWith } from 'jest-pact';

import { Discussions } from '../../../fixtures/project/merge_requests/discussions.fixture';
import { getDiscussions } from '../../../resources/api/project/merge_requests';

const CONSUMER_NAME = 'MergeRequests#show';
const PROVIDER_NAME = 'GET discussions';
const CONSUMER_LOG = '../logs/consumer.log';
const CONTRACT_DIR = '../contracts/project/merge_requests/show';

pactWith(
  {
    consumer: CONSUMER_NAME,
    provider: PROVIDER_NAME,
    log: CONSUMER_LOG,
    dir: CONTRACT_DIR,
  },

  (provider) => {
    describe(PROVIDER_NAME, () => {
      beforeEach(() => {
        const interaction = {
          ...Discussions.scenario,
          ...Discussions.request,
          willRespondWith: Discussions.success,
        };
        provider.addInteraction(interaction);
      });

      it('return a successful body', async () => {
        const discussions = await getDiscussions({
          url: provider.mockService.baseUrl,
        });

        expect(discussions).toEqual(Discussions.body);
      });
    });
  },
);

Writing consumer tests

Create the skeleton

The pactWith function

The PactOptions parameter

The PactFn parameter