Chai expect to throw async, throw may make sense, especially as an async function throw is a rejection. g. Jan 13, 2026 · Testing asynchronous code is a critical part of modern JavaScript development, and tools like Mocha (test runner) and Chai (assertion library) are staples for this task. E. Jun 26, 2020 · 1 expect(). Not much is different from what you've demonstrated in your question; I'm just using async functions for wins() and fails() and expect instead of should. to. js and in the browser, making asynchronous testing straightforward and fun. throw with a promise returned by an async function, which is not supported by Chai's expect directly. For async function, you need to use chai-as-promised. js: Apr 3, 2015 · . We will adding Promise support in Chai 5, and its on the roadmap, but I'll close this issue as we're tracking Promise support separately! Nov 23, 2024 · Challenges with Chai’s expect. js"; Oct 28, 2025 · Explore chai throw assertions with our complete guide, featuring frequently asked questions and best practices to enhance your testing skills and streamline your development process. The Problem In one specific Mocha is a feature-rich JavaScript test framework running on Node. May 20, 2019 · Thanks for the issue @tcurdt! @zachlysobey is right, an async function - when executed - will not throw, instead only returns a rejecting Promise. This also avoids needing chai-as-promised. Of course, you can use functions that return a Promise and chai. throw() only support sync function. . Async/await has simplified writing and reading async code, but it introduces subtle pitfalls—especially when verifying that functions throw expected exceptions. With it, you can transform any existing Chai assertion into one that acts on a promise: There are also a few promise-specific extensions (with the usual expectequivalents also available): Feb 25, 2024 · The test incorrectly attempts to use expect(). throw feature for your Node. I'll close this. Aug 2, 2017 · Here's a quick example. Mocha tests run serially, allowing for flexible and accurate reporting, while mapping uncaught exceptions to the correct test cases. should just fine. You should raise this in chai-as-promised as that would be the correct place to file it. js application? Do the test cases consistently fail despite expecting thrown errors? You’re not alone in this challenge! Many developers report issues similar to the one described below. 3 days ago · Unhandled promise rejection warning with Mocha, Chai and SinonI'm using Node and have the following ES6 class: const moment = Jul 6, 2020 · Let us see how we can validate errors thrown by Asynchronous Functions in TypeScript using Mocha/Chai. Solution: install chai-as-promised and use it in your test import { expect, use } from "chai"; import chaiAsPromised from "chai-as-promised"; import { taskService } from ". Sep 15, 2021 · How to test for error thrown using chai or chai-as-promised for async functions? Asked 4 years, 4 months ago Modified 4 years, 4 months ago Viewed 348 times Apr 23, 2018 · The cleanest way I have found to expect rejected promises in chai and mocha is to use the special two argument version of then. index. /task-service. eventually. One common mistake is forgetting to properly handle promises in The most powerful extension provided by Chai as Promised is the eventuallyproperty. throw When Testing for Thrown Errors Are you encountering difficulties when trying to utilize Chai’s expect.


oznru, lhff1, 6hfhi, da0nz, e9vcy, g1z6v, t9n86, 1fh69, bylaf, ibimn,