66 lines
2.3 KiB
Markdown
66 lines
2.3 KiB
Markdown
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[type-definitions]: https://github.com/facebook/jest/blob/main/packages/jest-types/src/Circus.ts
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<h1 align="center">
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<img src="https://jestjs.io/img/jest.png" height="150" width="150"/>
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<img src="https://jestjs.io/img/circus.png" height="150" width="150"/>
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<p align="center">jest-circus</p>
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<p align="center">The next-gen test runner for Jest</p>
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</h1>
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## Overview
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Circus is a flux-based test runner for Jest that is fast, maintainable, and simple to extend.
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Circus allows you to bind to events via an optional event handler on any [custom environment](https://jestjs.io/docs/configuration#testenvironment-string). See the [type definitions][type-definitions] for more information on the events and state data currently available.
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```js
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import {Event, State} from 'jest-circus';
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import NodeEnvironment from 'jest-environment-node';
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class MyCustomEnvironment extends NodeEnvironment {
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//...
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async handleTestEvent(event: Event, state: State) {
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if (event.name === 'test_start') {
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// ...
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}
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}
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}
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```
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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.
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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][type-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.
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## Installation
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> Note: As of Jest 27, `jest-circus` is the default test runner, so you do not have to install it to use it.
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Install `jest-circus` using yarn:
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```bash
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yarn add --dev jest-circus
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```
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Or via npm:
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```bash
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npm install --save-dev jest-circus
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```
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## Configure
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Configure Jest to use `jest-circus` via the [`testRunner`](https://jestjs.io/docs/configuration#testrunner-string) option:
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```json
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{
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"testRunner": "jest-circus/runner"
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}
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```
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Or via CLI:
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```bash
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jest --testRunner='jest-circus/runner'
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```
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