[QUESTION] How does one mock zip.js in Jest tests?

[remarkablemark]

I'm using zip.js in my frontend project and I'm trying to write Jest tests but they're failing with:

    ReferenceError: TransformStream is not defined

    > 1 | import { BlobReader, BlobWriter, ZipWriter } from '@zip.js/zip.js';
        | ^

I'm using jsdom for my test environment.

Is the best way to resolve this is to mock the node module? I have seen other projects provide a mock file for Jest.

[gildas-lormeau]

If the web steam API is not available, then you should able to circumvent this issue by importing this module before running the tests: https://www.npmjs.com/package/web-streams-polyfill

[janesenaj42]

Apparently TransformStream is available in Node 18 . But for anyone on Angular+Jest on older node versions, this worked for me in Node 14.15.5

// setup-jest.ts

import 'jest-preset-angular/setup-jest'
import { TransformStream } from 'web-streams-polyfill/ponyfill';

Object.defineProperties(globalThis, {
   TransformStream: {
      value: TransformStream
   }
}
```

[remarkablemark]

Thanks! I ended up creating a module mock for the package:

mkdir -p __mocks__/@zip.js/
echo "module.exports = {};" > __mocks__/@zip.js/zip.js.js