jest-circus

jest-circus

The next-gen test runner for Jest

Overview

Circus is a flux-based test runner for Jest that is fast, maintainable, and simple to extend.

Circus allows you to bind to events via an optional event handler on any custom environment. See the type definitions for more information on the events and state data currently available.

import type {Event, State} from 'jest-circus';
import {TestEnvironment as NodeEnvironment} from 'jest-environment-node';

class MyCustomEnvironment extends NodeEnvironment {
  //...

  async handleTestEvent(event: Event, state: State) {
    if (event.name === 'test_start') {
      // ...
    }
  }
}

Mutating event or state data is currently unsupported and may cause unexpected behavior or break in a future release without warning. New events, event data, and/or state data will not be considered a breaking change and may be added in any minor release.

Note, that jest-circus test runner would pause until a promise returned from handleTestEvent gets fulfilled. However, there are a few events that do not conform to this rule, namely: start_describe_definition, finish_describe_definition, add_hook, add_test or error (for the up-to-date list you can look at SyncEvent type in the types definitions). That is caused by backward compatibility reasons and process.on('unhandledRejection', callback) signature, but that usually should not be a problem for most of the use cases.

Installation

Note: As of Jest 27, jest-circus is the default test runner, so you do not have to install it to use it.

Install jest-circus using yarn:

yarn add --dev jest-circus

Or via npm:

npm install --save-dev jest-circus

Configure

Configure Jest to use jest-circus via the testRunner option:

{
  "testRunner": "jest-circus/runner"
}

Or via CLI:

jest --testRunner='jest-circus/runner'

Similar packages

Other packages similar to jest-circus

mocha

Mocha is a feature-rich JavaScript test framework running on Node.js and in the browser, making asynchronous testing simple. It's similar to jest-circus in providing a flexible and extensible testing framework, but differs in its execution model and default assertion library integration.

jasmine

Jasmine is a behavior-driven development framework for testing JavaScript code. It does not require a DOM, and it has a clean, obvious syntax so that you can easily write tests. Jasmine is similar to jest-circus in its syntax and approach to defining tests but operates independently of Jest and has its own assertion library.

ava

AVA is a test runner for Node.js with a concise API, detailed error output, and process isolation that lets you develop with confidence. It's similar to jest-circus in its focus on modern JavaScript features and concurrency but differs in its minimalistic approach and focus on speed.