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How to use takesDoneCallback method in Jest

Best JavaScript code snippet using jest

utils.js

Source:utils.js

...144});145const jestEachBuildDir = (0, _slash.default)(146  path.dirname(require.resolve('jest-each'))147);148function takesDoneCallback(fn) {149  return fn.length > 0;150}151function isGeneratorFunction(fn) {152  return (0, _isGeneratorFn.default)(fn);153}154const makeDescribe = (name, parent, mode) => {155  let _mode = mode;156  if (parent && !mode) {157    // If not set explicitly, inherit from the parent describe.158    _mode = parent.mode;159  }160  return {161    type: 'describeBlock',162    // eslint-disable-next-line sort-keys163    children: [],164    hooks: [],165    mode: _mode,166    name: (0, _jestUtil.convertDescriptorToString)(name),167    parent,168    tests: []169  };170};171exports.makeDescribe = makeDescribe;172const makeTest = (fn, mode, name, parent, timeout, asyncError) => ({173  type: 'test',174  // eslint-disable-next-line sort-keys175  asyncError,176  duration: null,177  errors: [],178  fn,179  invocations: 0,180  mode,181  name: (0, _jestUtil.convertDescriptorToString)(name),182  parent,183  seenDone: false,184  startedAt: null,185  status: null,186  timeout187}); // Traverse the tree of describe blocks and return true if at least one describe188// block has an enabled test.189exports.makeTest = makeTest;190const hasEnabledTest = describeBlock => {191  const {hasFocusedTests, testNamePattern} = (0, _state.getState)();192  return describeBlock.children.some(child =>193    child.type === 'describeBlock'194      ? hasEnabledTest(child)195      : !(196          child.mode === 'skip' ||197          (hasFocusedTests && child.mode !== 'only') ||198          (testNamePattern && !testNamePattern.test(getTestID(child)))199        )200  );201};202const getAllHooksForDescribe = describe => {203  const result = {204    afterAll: [],205    beforeAll: []206  };207  if (hasEnabledTest(describe)) {208    for (const hook of describe.hooks) {209      switch (hook.type) {210        case 'beforeAll':211          result.beforeAll.push(hook);212          break;213        case 'afterAll':214          result.afterAll.push(hook);215          break;216      }217    }218  }219  return result;220};221exports.getAllHooksForDescribe = getAllHooksForDescribe;222const getEachHooksForTest = test => {223  const result = {224    afterEach: [],225    beforeEach: []226  };227  let block = test.parent;228  do {229    const beforeEachForCurrentBlock = []; // TODO: inline after https://github.com/microsoft/TypeScript/pull/34840 is released230    let hook;231    for (hook of block.hooks) {232      switch (hook.type) {233        case 'beforeEach':234          beforeEachForCurrentBlock.push(hook);235          break;236        case 'afterEach':237          result.afterEach.push(hook);238          break;239      }240    } // 'beforeEach' hooks are executed from top to bottom, the opposite of the241    // way we traversed it.242    result.beforeEach = [...beforeEachForCurrentBlock, ...result.beforeEach];243  } while ((block = block.parent));244  return result;245};246exports.getEachHooksForTest = getEachHooksForTest;247const describeBlockHasTests = describe =>248  describe.children.some(249    child => child.type === 'test' || describeBlockHasTests(child)250  );251exports.describeBlockHasTests = describeBlockHasTests;252const _makeTimeoutMessage = (timeout, isHook) =>253  `Exceeded timeout of ${(0, _jestUtil.formatTime)(timeout)} for a ${254    isHook ? 'hook' : 'test'255  }.\nUse jest.setTimeout(newTimeout) to increase the timeout value, if this is a long-running test.`; // Global values can be overwritten by mocks or tests. We'll capture256// the original values in the variables before we require any files.257const {setTimeout, clearTimeout} = global;258function checkIsError(error) {259  return !!(error && error.message && error.stack);260}261const callAsyncCircusFn = (testOrHook, testContext, {isHook, timeout}) => {262  let timeoutID;263  let completed = false;264  const {fn, asyncError} = testOrHook;265  return new Promise((resolve, reject) => {266    timeoutID = setTimeout(267      () => reject(_makeTimeoutMessage(timeout, isHook)),268      timeout269    ); // If this fn accepts `done` callback we return a promise that fulfills as270    // soon as `done` called.271    if (takesDoneCallback(fn)) {272      let returnedValue = undefined;273      const done = reason => {274        // We need to keep a stack here before the promise tick275        const errorAtDone = new _jestUtil.ErrorWithStack(undefined, done);276        if (!completed && testOrHook.seenDone) {277          errorAtDone.message =278            'Expected done to be called once, but it was called multiple times.';279          if (reason) {280            errorAtDone.message +=281              ' Reason: ' +282              (0, _prettyFormat.format)(reason, {283                maxDepth: 3284              });285          }...

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.

Chapters

What is Jest Framework
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.
Jest Installation - All the prerequisites and set up steps needed to help you start Jest automation testing.
Using Jest with NodeJS Project - Learn how to leverage Jest framework to automate testing using a NodeJS Project.
Writing First Test for Jest Framework - Get started with code-based tutorial to help you write and execute your first Jest framework testing script.
Jest Vocabulary - Learn the industry renowned and official jargons of the Jest framework by digging deep into the Jest vocabulary.
Unit Testing with Jest - Step-by-step tutorial to help you execute unit testing with Jest framework.
Jest Basics - Learn about the most pivotal and basic features which makes Jest special.
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.
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. -

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

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.
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.
HTML Report Generation - Learn how to create a comprehensive HTML report based on your Jest test execution.
Testing React app using Jest Framework - Learn how to test your react web-application with Jest framework in this detailed Jest tutorial.
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.
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.
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.
Jest vs Mocha vs Jasmine - Learn the key differences between the most popular JavaScript-based testing frameworks i.e. Jest, Mocha, and Jasmine.
Jest FAQs(Frequently Asked Questions) - Explore the most commonly asked questions around Jest framework, with their answers.