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ts-jest is an npm package that allows users to run tests written in TypeScript directly, without having to precompile them to JavaScript. It is a Jest transformer with source map support that lets you use Jest to test projects written in TypeScript.
TypeScript testing
This feature allows you to write Jest tests in TypeScript. The code sample demonstrates a simple test for a sum function.
import sum from './sum';
test('adds 1 + 2 to equal 3', () => {
expect(sum(1, 2)).toBe(3);
});
Source map support
Source map support for accurate stack traces in error messages, which is useful for debugging tests.
/* Source maps are automatically handled by ts-jest, so there's no specific code sample for this feature. It works under the hood to provide accurate stack traces in your tests. */
TypeScript configuration
Allows you to use your project's TypeScript configuration or specify a custom one for testing purposes.
/* ts-jest uses the tsconfig.json file in your project to understand how to compile your TypeScript code. You can also specify a different configuration file for ts-jest if needed. */
Coverage reports
Integrates with Jest's coverage reporting to include TypeScript files in coverage statistics.
/* To collect coverage, you can use Jest's built-in coverage collection feature with ts-jest. */
jest --coverage
babel-jest is a Jest plugin that allows you to use Babel to transform your JavaScript code. It is similar to ts-jest but is focused on JavaScript with Babel transformations rather than TypeScript.
Jest itself is a testing framework that can work with TypeScript when configured with the appropriate preprocessor (like ts-jest). It provides the overall testing framework that ts-jest plugs into.
Mocha is another testing framework that can be used with TypeScript when combined with a TypeScript compiler like ts-node. It is an alternative to Jest and thus to ts-jest, but it requires additional setup for working with TypeScript.
karma-typescript is a Karma plugin that compiles and bundles TypeScript on the fly. It is similar to ts-jest in that it allows for testing TypeScript code, but it is designed to work within the Karma test runner ecosystem.
Note: Looking for collaborators. Want to help improve ts-jest?
From version "jest": "17.0.0"
we are using same MAJOR.MINOR as Jest
.
For "jest": "< 17.0.0"
use "ts-jest": "0.1.13"
. Docs for it see here.
To use this in your project, run:
npm install --save-dev ts-jest
Modify your project's package.json
so that the jest
section looks something like:
{
"jest": {
"transform": {
".(ts|tsx)": "<rootDir>/node_modules/ts-jest/preprocessor.js"
},
"testRegex": "(/__tests__/.*|\\.(test|spec))\\.(ts|tsx|js)$",
"moduleFileExtensions": [
"ts",
"tsx",
"js"
]
}
}
This setup should allow you to write Jest tests in Typescript and be able to locate errors without any additional gymnastics.
Prior to version 20.0.0
, coverage reports could be obtained using the inbuilt coverage processor in ts-jest
. Starting with version 20.0.0
, ts-jest
delegates coverage processing to jest and no longer includes a coverage processor.
To generate coverage results, set the mapCoverage
property in the jest
configuration section to true
.
Please note that the
outDir
property in thejest
configuration section is removed in coverage mode, due to #201.
There is a few additional steps if you want to use it with React Native.
Install babel-jest
and babel-preset-react-native
modules.
npm install -D babel-jest babel-preset-react-native
Ensure .babelrc
contains:
{
"presets": ["react-native"],
"sourceMaps": "inline"
}
In package.json
, inside jest
section, the transform
should be like this:
"transform": {
"^.+\\.js$": "<rootDir>/node_modules/babel-jest",
".(ts|tsx)": "<rootDir>/node_modules/ts-jest/preprocessor.js"
}
Fully completed jest section should look like this:
"jest": {
"preset": "react-native",
"transform": {
"^.+\\.js$": "<rootDir>/node_modules/babel-jest",
".(ts|tsx)": "<rootDir>/node_modules/ts-jest/preprocessor.js"
},
"testRegex": "(/__tests__/.*|\\.(test|spec))\\.(ts|tsx|js)$",
"moduleFileExtensions": [
"ts",
"tsx",
"js"
]
}
If only testing typescript files then remove the js
option in the testRegex.
You might want to use ES6 default imports, which will allow you to write things like
import React from 'react';
In that case you can add the following to your .tsconfig
"allowSyntheticDefaultImports": true
This will make ts-loader send the compiled typescript code through babel, and the above import will resolve.
This configuration will allow debugger
statements to work properly in both WebStorm and VSCode.
Breakpoints currently only work in WebStorm.
By default this package will try to locate tsconfig.json
and use its compiler options for your .ts
and .tsx
files.
But you are able to override this behaviour and provide another path to your config for TypeScript by using __TS_CONFIG__
option in globals
for jest
:
{
"jest": {
"globals": {
"__TS_CONFIG__": "my-tsconfig.json"
}
}
}
Or even declare options for tsc
instead of using separate config, like this:
{
"jest": {
"globals": {
"__TS_CONFIG__": {
"module": "commonjs",
"jsx": "react"
}
}
}
}
Note that if you haven't explicitly set the module
property in the __TS_CONFIG__
setting (either directly or through a separate configuration file), it will be overwritten to commonjs
(regardless of the value in tsconfig.json
) since that is the format Jest expects. This only happens during testing.
When using Jest with Angular (a.k.a Angular 2) apps you will likely need to parse HTML templates. If you're unable to add html-loader
to webpack config (e.g. because you don't want to eject from angular-cli
) you can do so by defining __TRANSFORM_HTML__
key in globals
for jest
.
{
"jest": {
"globals": {
"__TRANSFORM_HTML__": true
}
}
}
You'll also need to extend your transform
regex with html
extension:
{
"jest": {
"transform": {
"^.+\\.(ts|tsx|js|html)$": "<rootDir>/node_modules/ts-jest/preprocessor.js"
}
}
}
For all available options see TypeScript docs.
"target": "ES6"
while using node v4
in your test environment;"jsx": "preserve"
for now (see progress of this issue);"baseUrl": "<path_to_your_sources>"
, you also have to change jest config
a little bit:"jest": {
"moduleDirectories": ["node_modules", "<path_to_your_sources>"]
}
If you have any suggestions/pull requests to turn this into a useful package, just open an issue and I'll be happy to work with you to improve this.
git clone https://github.com/kulshekhar/ts-jest
cd ts-jest
npm install
npm test
Note: If you are cloning on Windows, you may have to run git config --system core.longpaths true
for Windows to stop complaining about long filenames.
Copyright (c) Authors. This source code is licensed under the MIT license.
FAQs
A Jest transformer with source map support that lets you use Jest to test projects written in TypeScript
The npm package ts-jest receives a total of 11,311,149 weekly downloads. As such, ts-jest popularity was classified as popular.
We found that ts-jest demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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