pact-js-mock

pact-js-mock is a Node.js library that allows you to build Pact contracts by leveraging your existings mocks. It could be used with your existing mocks defined with msw or Cypress. This library provides an easy way to generate contracts that can be used for testing and verifying API interactions between consumer and provider.

Install

yarn add -D pact-js-mock

Getting started with MSW and Jest

Here is an example of how to use pact-js-mock with MSW using Jest:

import { setupServer, rest } from 'msw/node'
import { Pact } from 'pact-js-mock/lib/msw'

import { reloadPact, deletePact, writePact } from 'pact-js-mock/lib/utils'
import { writeFile } from 'fs'

const server = setupServer()

const pact = new Pact(
  {
    consumer: { name: 'test-consumer' },
    provider: { name: 'rest-provider' },
    metadata: { pactSpecification: { version: '2.0.0' } },
  },
  {
    outputDir: 'pacts', // the pact is written by default to pacts folder
  },
)

before(() => {
  server.listen()
  deletePact(pact)
})

beforeEach(function () {
  // set the current test name as the source of the pact
  pact.setCurrentSource(this.currentTest.title)
  reloadPact(pact)
})

afterEach(() => {
  server.resetHandlers()
  writePact(pact)
})

after(() => {
  server.close()
})

it('get all movies', async () => {
  const mockMovies = rest.get(
    '*/movies',
    pact.toResolver({
      description: 'a request to list all movies',
      response: [
        {
          id: 1,
          name: 'Movie 1',
          year: 2008,
        },
        {
          id: 2,
          name: 'Movie 2',
          year: 2008,
        },
      ],
    }),
  )

  server.use(mockMovies)

  const movies = await fetchMovies()

  expect(movies).toEqual([
    {
      id: 1,
      name: 'Movie 1',
      year: 2008,
    },
    {
      id: 2,
      name: 'Movie 2',
      year: 2008,
    },
  ])
})

You can find more example to mock

• A Rest API
• A GraphQL API

Getting started with MSW and Mocha

Here is an example of how to use pact-js-mock with MSW using Jest:

import { setupServer, rest } from 'msw/node'
import { Pact } from 'pact-js-mock/lib/msw'

import { reloadPact, deletePact, writePact } from 'pact-js-mock/lib/utils'
import { writeFile } from 'fs'

const server = setupServer()

const pact = new Pact(
  {
    consumer: { name: 'test-consumer' },
    provider: { name: 'rest-provider' },
    metadata: { pactSpecification: { version: '2.0.0' } },
  },
  {
    outputDir: 'pacts', // the pact is written by default to pacts folder
  },
)

before(() => {
  server.listen()
  deletePact(pact)
})

beforeEach(function () {
  // set the current test name as the source of the pact
  pact.setCurrentSource(this.currentTest.title)
  reloadPact(pact)
})

afterEach(() => {
  server.resetHandlers()
  writePact(pact)
})

after(() => {
  server.close()
})

it('get all movies', async () => {
  const mockMovies = rest.get(
    '*/movies',
    pact.toResolver({
      description: 'a request to list all movies',
      response: [
        {
          id: 1,
          name: 'Movie 1',
          year: 2008,
        },
        {
          id: 2,
          name: 'Movie 2',
          year: 2008,
        },
      ],
    }),
  )

  server.use(mockMovies)

  const movies = await fetchMovies()

  expect(movies).toEqual([
    {
      id: 1,
      name: 'Movie 1',
      year: 2008,
    },
    {
      id: 2,
      name: 'Movie 2',
      year: 2008,
    },
  ])
})

Getting started with Cypress

Here is an example of how to use pact-js-mock with Cypress:

Setup Pact

Write a file named pact.js for example

import { Pact } from 'pact-js-mock/lib/cypress'

export const pact = new Pact(
  {
    consumer: { name: 'test-consumer' },
    provider: { name: 'rest-provider' },
    metadata: { pactSpecification: { version: '2.0.0' } },
  },
  {
    outputDir: 'pacts', // the pact is written by default to pacts folder
  },
)

Setup Cypress commands

Two Cypress functions are available with this module cy.reloadPact() and cy.writePact(), import the module pact-js-mock/lib/cypress/commands in the file cypress/support/commands.(js|ts)

// cypress/support/commands.js
import 'pact-js-mock/lib/cypress/commands'

before(() => {
  // To persist recorded interaction between each tests, add this
  cy.reloadPact(pact)
})

beforeEach(() => {
  // set the current test name as the source of the pact
  pact.setCurrentSource(Cypress.currentTest.title)
})

after(() => {
  // Write the pact file after each Cypress test
  cy.writePact(pact)
})

Setup Cypress plugin

Import this in the cypress/plugins/index.js

// cypress/plugins/index.js

import pactPlugin from 'pact-js-mock/lib/cypress/plugin'

module.exports = (on, config) => {
  config = pactPlugin(on, config)
  return config
}

Write a sample test

it('get all movies', async () => {
  // intercept and mock the movies response while record the interaction
  cy.intercept(
    'GET',
    `/*/movies`,
    pact.toHandler({
      description: 'a request to list all movies',
      response: [
        {
          id: 1,
          name: 'Movie 1',
          year: 2008,
        },
        {
          id: 2,
          name: 'Movie 2',
          year: 2008,
        },
      ],
    }),
  ).as('multipleMovies')

  // open the page to test
  cy.visit('/')

  // add your assertions
  cy.wait('@multipleMovies')
    .its('response')
    .its('statusCode')
    .should('be.equal', 200)
})

You can find more example to mock

• A Rest API
• A GraphQL API

Author

👤 Ludovic Dorival

• Github: @ludorival

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📝 License

Copyright © 2021 Ludovic Dorival. This project is BSD--3--Clause licensed.

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