Typescript Jest Types not Found

If you are a Typescript developer using Jest for testing, you may see an error that says "Jest encountered an unexpected token. This usually means that you are trying to import a file which Jest cannot parse, e.g. it's not plain JavaScript." This error message is usually caused by missing type declarations.

To solve this issue, you need to make sure that Jest can find the type declarations for your Typescript code. Here are a few steps you can take:

1. Install @types/jest package

You need to install the @types/jest package as a dev dependency. This package provides type declarations for Jest.

npm install --save-dev @types/jest

2. Update jest.config.js

In your jest.config.js file, add the following line to tell Jest where to find the type declarations:

module.exports = {
  // ...
  globals: {
    'ts-jest': {
      tsconfig: 'path/to/tsconfig.json',
    },
  },
};

Replace 'path/to/tsconfig.json' with the path to your tsconfig.json file.

3. Update tsconfig.json

In your tsconfig.json file, make sure that the types property includes 'jest':

{
  "compilerOptions": {
    // ...
    "types": [
      // ...
      "jest"
    ]
  }
}

4. Restart Jest

After making these changes, you need to restart Jest.

With these steps, you should be able to resolve the "Jest encountered an unexpected token" error caused by missing type declarations in your Typescript code.

Conclusion

In this article, we have seen how to resolve the "Typescript Jest Types not Found" error by configuring Jest to find type declarations for Typescript code. By following these steps, you should be able to get Jest working with your Typescript codebase without any issues.