Facebook's Jest testing framework is easy to get started with, but the documentation overlooks an annoying aspect: test statements will be highlighted as errors by any editor that tries to warn of undefined symbols, because test
, expect
, and all matcher methods are not defined.
Similary, attempting to run a test file with node
directly will fail with ReferenceError: test is not defined
.
What require
/import
statement(s) need to be added for those errors to go away?
By default, Jest runs all your tests and shows their result in the console. Yet, Jest comes with a bail option allowing you to stop running tests after n failed tests. You may configure the bail option to a boolean value or a number. Using a boolean for bail will either stop or not stop after the first failed test.
Jest is a JavaScript testing framework designed to ensure correctness of any JavaScript codebase. It allows you to write tests with an approachable, familiar and feature-rich API that gives you results quickly. Jest is well-documented, requires little configuration and can be extended to match your requirements.
To speed-up your tests, Jest can run them in parallel. By default, Jest will parallelise tests that are in different files. IMPORTANT: Paralellising tests mean using different threads to run test-cases simultaneously. Figure 2.
If you want to run them directly through node, try to require Also give jest
and/or jest-runtime
.@types/jest
a try as well.
Check Edit 2 for new info about this
Edit
@types/jest
(jest-DefinitelyTyped
) is definitely needed (or just one solution). If you install it (e.g., dev dependency), the IDE errors should go away. I just tried it on Webstorm, and it works.
Edit 2
The new Jest@20 Matchers (e.g., .resolves
and .rejects
) are still not defined in @types/jest
. You can keep track of its status on the links below: https://github.com/DefinitelyTyped/DefinitelyTyped/pull/16645 https://github.com/DefinitelyTyped/DefinitelyTyped/issues/16803
It should be available soon, though!
Also, it doesn't seem possible to run it directly through node. Last night I tried a bunch of different things, but using jest is the way to go - it really uses node under the hood, so I thought it would be possible as well. @thymikee over your opened issue at GitHub made clear that it's not.
Edit 3
The new release (20.0.1) includes the newest Jest definitions.
this isn't in the scope of this specific problem, but it also helps
Are you using something like ESLint? If so, you'll need eslint-plugin-jest
Following the steps described in this page: https://www.npmjs.com/package/eslint-plugin-jest, you will basically need to add it as an ESLint plugin and set jest globals in the ESLint configuration:
{ "env": { "jest/globals": true } }
If you plan on supporting ES6 tests, you'll also need Babel
and babel-jest
plugin with the following jest configuration:
"transform": { "^.+\\.js$": "babel-jest" }
Finally, for Typescript tests you'd need the @types/jest
and ts-jest
packages as well
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