Configure Jest global tests setup with .ts file (TypeScript)

For anyone with TS error with @remeus's answer, the following change will do the trick:

require('ts-node').register({
  transpileOnly: true,
});

If you're using absolute imports, use this:

require('tsconfig-paths').register();

I found a solution.

My initial project structure was:

.
|--src
|  |--service.ts
|--tests
|  |--service.test.ts
|--dist
|--tsconfig.json 
|--package.json

Jest configuration in package.json:

"jest": {
  "globals": {
    "ts-jest": {
      "tsconfig": "tsconfig.json"
    }
  },
  "moduleFileExtensions": ["ts","js"],
  "transform": {
    "^.+\\.(ts|tsx)$": "./node_modules/ts-jest/preprocessor.js"
  },
  "testMatch": [
    "**/tests/**/*.test.(ts|js)"
  ],
  "testEnvironment": "node"
}

With this configuration ts-jest perform in memory transpiling of the .ts files. I have outDir option in compilerOptions of my tsconfig.json, but nothing is written in that outDir and because I cann't use transpiled jest-config.js

Then I move tests folder in src and change Jest config. New structure of the project is:

.
|--src
|  |--service.ts
|  |--tests
|     |--service.test.ts
|     |--jest-config.ts
|--dist
|--tsconfig.json 
|--package.json

New Jest config is:

"jest": {
  "globalSetup": "./dist/tests/jest-config.js",
  "moduleFileExtensions": ["ts", "js", "json"],
  "testMatch": [
    "**/dist/**/*.test.js"
  ],
  "testEnvironment": "node"
}

Now I can use jest-config.js for global setup in Jest.

Addition

• Jest setup file (in my example jest-config.js) must export one async function:

  module.exports = async function() { ... }

• Before running the tests, you need to compile source .ts files.

Global setup is performed before a ts environment is made available, so a workaround is to create the environment manually by requiring ts-node at the beginning of the file.

In your jest configuration (package.json or jest.config.js):

"globalSetup": "./globalSetup.ts"

Then in globalSetup.ts:

require('ts-node/register');

const setup = (): void => {
  // whatever you need to setup globally
};

export default setup;

You can read more about ts-node on github.