Why isn't my asynchronous Jest test throwing the expected failure?

I am facing an issue while testing asynchronous actions using Jest. Currently, my test is passing when it should actually fail.

describe('Asynchronous Code', () => {
  it('should execute promise', () => {
    console.log(1);
    someFunctionThatReturnsAPromise()
      .then(() => {
        console.log(2);
        expect(true).toBeFalsy();
        console.log(3);
      });
    console.log(4);
  });
});

After running npm test, the output shows:

PASS  __tests__/Async.test.js
 ● Console

   console.log __tests__/Async.test.js:3
     1
   console.log static-content-test/react/actions/DashboardActions.test.js:6
     2
   console.log static-content-test/react/actions/DashboardActions.test.js:10
     4

Although the test passes, console.log(3) is not executed as expected due to the failed assertion of true being falsy.

I am seeking guidance on how to make Jest recognize expectations within async callbacks properly.

Answer №1

When conducting tests on asynchronous code, it is essential to ensure that the promise is returned from the test. Modify the test body as follows:

return executeAsyncFunction()
  .then(() => {
    expect(true).toBeFalsy();
  });

By implementing this change, the test will fail as anticipated:

FAIL  __tests__/Async.test.js
 ● Asynchronous Code › should run promise

   expect(received).toBeFalsy()

   Expected value to be falsy, received
     true

Facebook's preferred method for testing asynchronous code using jest can be found here.

Answer №2

Another approach is to utilize the done pattern outlined in this post:

it('should run promise', (done) => {
  someFunctionThatReturnsAPromise()
    .then(() => {
      expect(true).toBeFalsy();
      done();
    });
});

This method is compatible with Jest, but is more commonly associated with Jasmine and Mocha.

Answer №3

Discovering an alternative approach.

Jest will come to an end once it reaches the conclusion of the context. To ensure Jest waits for the promise to be resolved and tested, you must return the promise from the callback function.

Suppose we have a promise

const promise=fetch("blah.com/api")

test("should return valid data",()=>{
   return expect(promise).resolves.toBeTruthy() 
})

.resolves is used to await the resolution of the promise, after which you can apply suitable matchers as needed.

Additionally, you can employ .rejects when assessing error scenarios.

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Troubleshooting Bootstrap 3.0: Issues with nav-tabs not toggling

I have set up my navigation tabs using Bootstrap 3 in the following way: <ul class="nav nav-tabs pull-right projects" role="tablist" style="margin-top:20px;"> <li class="active"><a role="tab" data-toggle="tab" href="#progress">In Pr ...

Unable to send post parameters to Yii2 controller using an XHR request

Within the context of my project, I am making an xhr request to a yii2 controller. Here is how the request is structured in my view: var xhr = new XMLHttpRequest(); xhr.open('POST', '$urlToController', true); xhr.setRequestHeader("Co ...

Encountered an eas error during Android build process

When I try to execute the command "eas build --platform android" I encounter the following error message: "✖ Build failed ...

What is the best way to handle reading hefty files using the fs.read method and a buffer in JavaScript?

I'm currently delving into the world of javascript, and one of my go-to exercises when learning a new programming language is to create a hex-dump program. The main requirements for this program are: 1. to read a file provided through the command line ...

Utilizing HTML5 Canvas for Shadow Effects with Gradients

Surprisingly, it seems that the canvas API does not support applying gradients to shadows in the way we expect: var grad = ctx.createLinearGradient(fromX, fromY, toX, toY); grad.addColorStop(0, "red"); grad.addColorStop(1, "blue"); ctx.strokeStyle = gra ...

What is the correct way to assign an image to a state and function?

Hello, I am new to programming and I am eager to create a function that can dynamically change 3 images based on a random number. For example, I want it to work like this: if the number generated is greater than 5, display image1; if the number is greater ...

What is causing the issue with the height resizing in this procedure?

I've defined a process: jQuery(window).load(function() { function equalizeChildrenHeight() { jQuery('.children-have-equal-height').each(function(){ var children = jQuery(this).children(); var numChildr ...

What is the process for activating a script file once I have replaced HTML content using a backend method?

After receiving HTML content from the backend, including the <script> tags, I noticed that the scripts.js file does not seem to be activated. While the HTML content displays fine, changing the path to style.css successfully alters the appearance of ...

Command to conceal components for users visiting as guests

I'm looking to develop a directive that hides specific elements for guest users. Here is the current code I have: angular.module('someMod') .directive('premiumUser', premiumUser) .controller('PremiumUserCtrl', Pr ...

Angular ng-boostrap modal automatically refreshes upon detecting mouse movement with an embedded video

Currently, I am facing an issue with my Angular 7 ng-bootstrap modal. The problem arises when the modal, which includes a video player within an <iframe>, is moved to the production system. Whenever there is any mouse movement detected, the video get ...

What could be causing my jQuery to suddenly stop functioning?

My website has a simple jQuery function that expands information divs. It was working perfectly fine until the other day when I made some changes to my site (not related to the jQuery) and now it's suddenly not working at all, and I can't figure ...

Can pure Javascript be used to integrate Bootstrap pagination into a Bootstrap table?

I have created a custom JavaScript code to generate a Bootstrap table with hardcoded values. Now, I am looking to implement Bootstrap pagination using JavaScript only. var table = document.createElement("table"); table.className = "table"; var the ...

Angular Material UI dropdown menu

Currently, I am in the process of incorporating a select dropdown using Angular Material UI. <md-select class="width-100" placeholder="Priority" data-ng-model="task.priority"> <md-option value="one">One</md-option> <md-option ...

Can loading data after the initial page load improve the performance of web page loading?

Is it beneficial to load non-essential data using AJAX immediately after the page loads in order to speed up overall webpage loading time? There are certain modules on my website that are not crucial, so I am currently waiting for the basic content to loa ...

The serialization method in ajax is not providing the expected values as needed

Having trouble retrieving all the necessary form inputs using AJAX, jQuery, and Bootstrap modal. The serialize method is not returning all the required values. Specifically, I am missing the user_id and btn_action values. What could be the issue? I'v ...

What steps should I take to make this slider functional?

How can I achieve a sliding effect on this code? I want the div to slide out when the button is clicked, but I also want the button itself to move. Additionally, how can I ensure that the image and text are displayed in two columns? In my IDE, it appears a ...

How can one transform an array (in the form of a JSON array) into a map?

After running my script, I receive an array (JSON Array) structured like this: [{redirectCount=0, encodedBodySize=60962, unloadEventEnd=0, responseEnd=1601.699999999255, domainLookupEnd=995.7999999896856, ... Now, I want to display the key-value pairs fr ...

Can a directive be designed to function as a singleton?

Our large single page app includes a directive that is utilized in various locations across the page, maintaining its consistent behavior and appearance each time. However, we are experiencing an issue with this directive due to the ng-repeat it contains, ...

Error: The `gatsby require.resolve` function cannot locate the specified module when attempting

Currently, I am referring to the tutorial at and have already set up my gatsby-node.js file. Here is how my current directory structure looks like: public src -pages -templates --program_group.js static gatsby-config.js gatsby-node.js In my gatsby-node. ...

jQuery unable to find designated elements in uploaded templates

I have a specific route linked to a specific controller and view: app.config(['$routeProvider', function ($routeProvider) { $routeProvider .when('/create', { templateUrl: 'partials/form/form.html', controlle ...