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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?
ts-jest is a TypeScript preprocessor with source map support for Jest that lets you use Jest to test projects written in TypeScript.
To use this in your project, run:
npm install --save-dev ts-jest @types/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",
"jsx",
"json"
]
}
}
This setup should allow you to write Jest tests in Typescript and be able to locate errors without any additional gymnastics.
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.
You can try using ts-jest with jest@test
; use at your own risk! (And file an issue if you find problems.)
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.
ts-jest tries to ship with sensible defaults, to get you on your feet as quickly as possible.
Sourcemaps should work out of the box. That means your stack traces should have the correct line numbers, and you should be able to step through the TypeScript code using a debugger.
ts-jest automatically located your tsconfig
file.
If you want to compile typescript with a special configuration, you can do that too
If you're on a codebase where you're using synthetic default imports, e.g.
//Regular imports
import * as React from 'react';
//Synthetic default imports:
import React from 'react';
ts-jest tries to support that. If allowSyntheticDefaultImports
is set to true in your tsconfig
file, it uses babel
to automatically create the synthetic default exports for you - nothing else needed.
You can opt-out of this behaviour with the skipBabel flag
Just like Jest ts-jest
automatically uses babel to hoist your jest.mock()
calls to the top of your file.
You can opt-out of this behaviour with the skipBabel flag
If the default setup doesn't address your requirements, you can create a custom setup to suit your project.
By default this package will try to locate tsconfig.json
and use its compiler options for your .ts
and .tsx
files.
You can override this behaviour by pointing ts-jest to a custom TypeScript configuration file.
You can do this by setting the tsConfigFile
option in your global variables under the ts-jest
key to path of the
custom configuration file (relative to the project's root directory)
{
"jest": {
"globals": {
"ts-jest": {
"tsConfigFile": "my-tsconfig.json"
}
}
}
}
Warning: Using __TS_CONFIG__ option in globals is deprecated and soon will be removed.
For all available tsc
options see TypeScript docs.
Note that if you haven't explicitly set the module
property through a separate configuration file with tsConfigFile
, 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.
If you don't use mocks, or synthetic default imports you can skip the babel-transpilation step.
This means jest.mock()
calls will not be hoisted to the top,
and synthetic default exports will never be created.
Simply add skipBabel to your global variables under the ts-jest
key:
//This will skip babel transpilation
{
"jest": {
"globals": {
"ts-jest": {
"skipBabel": true
}
}
}
}
.babelrc
When using Babel, ts-jest, by default, doesn't use the .babelrc
file. If you want ts-jest to use .babelrc
, you should set the globals > ts-jest > useBabelrc
flag to true
in your jest
configuration.
{
"jest": {
"globals": {
"ts-jest": {
"useBabelrc": true
}
}
}
}
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.
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"
}
}
}
If you have dependencies on npm packages that are written in TypeScript but are
not published in ES5 you have to tweak your configuration. For example
you depend on a private scoped package @foo/bar
you have to add following to
your Jest configuration:
{
// ...
"transformIgnorePatterns": [
"<rootDir>/node_modules/(?!@foo)"
]
// ...
}
By default Jest ignores everything in node_modules
. This setting prevents Jest from ignoring the package you're interested in, in this case @foo
, while continuing to ignore everything else in node_modules
.
"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>"]
}
tsc --noEmit -p . && jest
If the jest.mock()
calls is placed after actual code, (e.g. after functions or classes) and skipBabel
is not set,
the line numbers in stacktraces will be off.
We suggest placing the jest.mock()
calls after the imports, but before any actual code.
const enum
is not supportedThis is due to a limitation in the ts-jest preprocessor which compiles each test file individually, therefore ignoring implementations of ambient declarations. The TypeScript team currently have no plan to support const enum inlining for this particular compiler method. See #112 and #281 for more information.
One possible workaround is to manually inline usage of const enum values - i.e. in your code, use let x: Enum = 1 as Enum
as opposed to let x: Enum = Enum.FirstValue
. This allows you to keep the type checking on enums without running into this issue.
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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