How to use testJestWorker method in Jest

Best JavaScript code snippet using jest


Source:test.js Github


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...58 promisified.then(countToFinish);59 }60 });61}62function testJestWorker() {63 return new Promise(async (resolve, reject) => {64 const startTime =;65 let count = 0;66 async function countToFinish() {67 if (++count === calls) {68 farm.end();69 const endTime =;70 // Let all workers go down.71 await sleep(2000);72 resolve({73 globalTime: endTime - startTime - 2000,74 processingTime: endTime - startProcess,75 });76 }77 }78 const farm = new JestWorker(require.resolve('./workers/jest_worker'), {79 exposedMethods: [method],80 forkOptions: {execArgv: []},81 workers: threads,82 });83 farm.getStdout().pipe(process.stdout);84 farm.getStderr().pipe(process.stderr);85 // Let all workers come up.86 await sleep(2000);87 const startProcess =;88 for (let i = 0; i < calls; i++) {89 const promisified = farm[method]();90 promisified.then(countToFinish);91 }92 });93}94function profile(x) {95 console.profile(x);96}97function profileEnd(x) {98 console.profileEnd(x);99}100async function main() {101 if (!global.gc) {102 console.log('GC not present');103 }104 const wFResults = [];105 const jWResults = [];106 for (let i = 0; i < 10; i++) {107 console.log('-'.repeat(75));108 profile('worker farm');109 const wF = await testWorkerFarm();110 profileEnd('worker farm');111 await sleep(3000);112 // eslint-disable-next-line no-undef113 global.gc && gc();114 profile('jest worker');115 const jW = await testJestWorker();116 profileEnd('jest worker');117 await sleep(3000);118 // eslint-disable-next-line no-undef119 global.gc && gc();120 wFResults.push(wF);121 jWResults.push(jW);122 console.log('jest-worker:', jW);123 console.log('worker-farm:', wF);124 }125 let wFGT = 0;126 let wFPT = 0;127 let jWGT = 0;128 let jWPT = 0;129 for (let i = 0; i < 10; i++) {...

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Jest Testing Tutorial

LambdaTest’s Jest Testing Tutorial covers step-by-step guides around Jest with code examples to help you be proficient with the Jest framework. The Jest tutorial has chapters to help you learn right from the basics of Jest framework to code-based tutorials around testing react apps with Jest, perform snapshot testing, import ES modules and more.


  1. What is Jest Framework
  2. Advantages of Jest - Jest has 3,898,000 GitHub repositories, as mentioned on its official website. Learn what makes Jest special and why Jest has gained popularity among the testing and developer community.
  3. Jest Installation - All the prerequisites and set up steps needed to help you start Jest automation testing.
  4. Using Jest with NodeJS Project - Learn how to leverage Jest framework to automate testing using a NodeJS Project.
  5. Writing First Test for Jest Framework - Get started with code-based tutorial to help you write and execute your first Jest framework testing script.
  6. Jest Vocabulary - Learn the industry renowned and official jargons of the Jest framework by digging deep into the Jest vocabulary.
  7. Unit Testing with Jest - Step-by-step tutorial to help you execute unit testing with Jest framework.
  8. Jest Basics - Learn about the most pivotal and basic features which makes Jest special.
  9. Jest Parameterized Tests - Avoid code duplication and fasten automation testing with Jest using parameterized tests. Parameterization allows you to trigger the same test scenario over different test configurations by incorporating parameters.
  10. Jest Matchers - Enforce assertions better with the help of matchers. Matchers help you compare the actual output with the expected one. Here is an example to see if the object is acquired from the correct class or not. -

|<p>it('check_object_of_Car', () => {</p><p> expect(newCar()).toBeInstanceOf(Car);</p><p> });</p>| | :- |

  1. Jest Hooks: Setup and Teardown - Learn how to set up conditions which needs to be followed by the test execution and incorporate a tear down function to free resources after the execution is complete.
  2. Jest Code Coverage - Unsure there is no code left unchecked in your application. Jest gives a specific flag called --coverage to help you generate code coverage.
  3. HTML Report Generation - Learn how to create a comprehensive HTML report based on your Jest test execution.
  4. Testing React app using Jest Framework - Learn how to test your react web-application with Jest framework in this detailed Jest tutorial.
  5. Test using LambdaTest cloud Selenium Grid - Run your Jest testing script over LambdaTest cloud-based platform and leverage parallel testing to help trim down your test execution time.
  6. Snapshot Testing for React Front Ends - Capture screenshots of your react based web-application and compare them automatically for visual anomalies with the help of Jest tutorial.
  7. Bonus: Import ES modules with Jest - ES modules are also known as ECMAScript modules. Learn how to best use them by importing in your Jest testing scripts.
  8. Jest vs Mocha vs Jasmine - Learn the key differences between the most popular JavaScript-based testing frameworks i.e. Jest, Mocha, and Jasmine.
  9. Jest FAQs(Frequently Asked Questions) - Explore the most commonly asked questions around Jest framework, with their answers.

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