ts-jest

What is ts-jest?

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.

What are ts-jest's main functionalities?

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

Other packages similar to ts-jest

babel-jest

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

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

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

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.

README

ts-jest

Table of Contents

• Versioning
• Usage
• Options
• How to Contribute
  • Quickstart to run tests (only if you're working on this package)
• License

Versioning

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.

Usage

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.

By default jest does not provide code coverage remapping for transpiled codes, so if you'd like to have code coverage it needs additional coverage remapping. This can be done via writing custom processing script, or configure testResultsProcessor to use built-in coverage remapping in ts-jest.

{
  "jest": {
    "transform": {
      ".(ts|tsx)": "<rootDir>/node_modules/ts-jest/preprocessor.js"
    },
    "testResultsProcessor": "<rootDir>/node_modules/ts-jest/coverageprocessor.js"
  }
}

Note: If you're experiencing remapping failure with source lookup, it may due to pre-created cache from jest. It can be manually deleted, or execute with --no-cache to not use those.

Options

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"
      }
    }
  }
}

For all available options see TypeScript docs.

Note: You can't target ES6 while using node v4 in your test environment.

How to Contribute

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.

Quickstart to run tests (only if you're working on this package)

git clone https://github.com/kulshekhar/ts-jest
cd ts-jest
npm install
npm test

License

Copyright (c) Authors.
This source code is licensed under the MIT license.

Changelog

17.0.2 (2016-12-01)

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