gulp-multi-thread-task/test/lib/message-handlers.test.js

Takes a gulp task and make's it run in multiple threads to improve build time

const path = require('path');
const cluster = require('cluster');
const {masterMessageHandlers} = require('../../lib/message-handlers');

describe('message-handlers', () => {
  test(('testing getFile being called number of time equal to processedGlobArray.length + 1'), () => {
    cluster.setupMaster({
      exec: path.resolve(__dirname + '/__mocks__/message-handlers-mock.js'),
    });
    const worker = cluster.fork();

    // generate a random array size each time for test to validate getFile is called correct number of times regardless of array size
    const processArrayGlobSize = Math.floor(Math.random() * 10) + 1;
    const processedGlobArray = Array.from(
        {length: processArrayGlobSize}, () => 'fakeFile',
    );

    const handlers = masterMessageHandlers(processedGlobArray);
    const getFileSpy = jest.spyOn(handlers, 'getFile');

    return new Promise((resolve, reject) => {
      worker.on('message', (message) => {
        handlers[message.type](worker, message, reject);
      });
      worker.on('exit', resolve);
      worker.on('error', reject);
    })
        .then(() => expect(getFileSpy)
            .toHaveBeenCalledTimes(processArrayGlobSize + 1));
  });

  test(('testing workerError being called from child worker'), () => {
    cluster.setupMaster({
      exec: path.resolve(
          __dirname + '/__mocks__/message-handlers-error-mock.js',
      ),
    });
    const worker = cluster.fork();

    const handlers = masterMessageHandlers([]);
    const workerErrorSpy = jest.spyOn(handlers, 'workerError');

    return new Promise((resolve, reject) => {
      worker.on('message', (message) => {
        handlers[message.type](worker, message, reject);
      });
      worker.on('exit', resolve);
      worker.on('error', reject);
    })
        .catch(() => expect(workerErrorSpy).toHaveBeenCalledTimes(1));
  });
});