Error Type: Jest: A transform is required to have a `process` function in order for it to

Encountering an error while running 'npm test':

 FAIL  __tests__/unit/domain/services/demo-service.ts
  ● Test suite failed to run

    TypeError: Jest: a transform must export a `process` function.

      at ScriptTransformer._getTransformer (node_modules/@jest/transform/build/ScriptTransformer.js:357:15)
      at ScriptTransformer.transformSource (node_modules/@jest/transform/build/ScriptTransformer.js:419:28)
      at ScriptTransformer._transformAndBuildScript (node_modules/@jest/transform/build/ScriptTransformer.js:523:40)
      at ScriptTransformer.transform (node_modules/@jest/transform/build/ScriptTransformer.js:579:25)
typescriptnpmjestjs

Answer №1

In order to ensure compatibility, the major version of <code>ts-jest
must align with the major version of jest.

{
  "devDependencies": {
    "jest": "^26.4.2",
    "ts-jest": "^26.3.0"
  }
}

Answer №2

It seems like the problem may lie with the version of jest. I personally had success using version 26.5.5.

If you are working with npm, there are a few packages that might help resolve the issue:

npm install <a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="39535c4a4d790b0f170c170c">[email protected]</a> --save-dev
npm install ts-jest --save-dev
npm install ts-node --save-dev
npm install ts-loader --save-dev

Answer №3

In my particular scenario, I opted for using babel-jest along with @babel/preset-typescript instead of ts-jest.

As a result, it was crucial to ensure that both babel-jest and jest were on the same major version.

{
  "devDependencies": {
    "@babel/preset-typescript": "7.16.7",
    "babel-jest": "26.6.3",
    "jest": "26.6.3"
  }
}

Answer №4

Initially, I was using jest version 24.x.x. The transformer issue arose when I upgraded to version 27.5.1.

Since my project wasn't TypeScript-based, I didn't have a dependency on ts-jest. To resolve the problem, I made adjustments to the

transform: {
    '^.+\\.js$': 'babel-jest',
    '^.+\\.(css|scss)$': 'jest-css-module',
  },

by updating it to

transform: {
    '^.+\\.js$': 'babel-jest',
    '^.+\\.(css|scss)$': 'jest-css-modules-transform', // modification made here
  },

Additionally, I included

testEnvironment: 'jsdom',

in the jest configuration as Jest now offers support for testing in different environments (this feature was not available in version 24.x.x).

If you write a test that requires the node environment, you will need to install the core-js package and use import in the specific test file.

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