freeCodeCamp/probot/test/index.test.js

const expect = require('expect')
const { Probot } = require('probot')
const prSuccessEvent = require('./events/pullRequests.opened')
const prExisting = require('./events/pullRequests.existing')
const probotPlugin = require('..')

describe('Presolver', () => {
  let probot, github

  beforeEach(() => {
    probot = new Probot({})
    // Load our app into probot
    let app = probot.load(probotPlugin)
    // This is an easy way to mock out the GitHub API
    // https://probot.github.io/docs/testing/
    github = {
      issues: {
        createComment: jest.fn().mockReturnValue(Promise.resolve({})),
        addLabels: jest.fn(),
        getLabel: jest.fn().mockImplementation(() => Promise.resolve([])),
        createLabel: jest.fn()
      },
      repos: {
        getContent: () => Promise.resolve({data: Buffer.from(`
          issueOpened: Message  
          pullRequestOpened: Message
          `).toString('base64')})
      },
      pullRequests: {
        getFiles: jest.fn().mockImplementation(() => ({
          data: [
            {filename: 'test.txt'}
          ]
        })),
        getAll: jest.fn().mockImplementation(() => ({ data: [prExisting.pull_request] }))
      }
    }
    app.auth = () => Promise.resolve(github)
    // just return a test token
    // app.app = () => 'test'
  })

  test('adds a label if a PR has changes to files targeted by an existing PR', async () => {
    // Receive a webhook event
    await probot.receive({name: 'pull_request.opened', payload: prSuccessEvent})
    expect(github.issues.addLabels).toHaveBeenCalled()
  })
})

// For more information about testing with Jest see:
// https://facebook.github.io/jest/

// For more information about testing with Nock see:
// https://github.com/nock/nock