Unit testing functions that use workerize'd imports

[wbobeirne]

Has anyone come up with a way to write unit tests (e.g. jest, mocha) for functions that user workerize-loader imports? It'd be great if there was an easy way to replace the default workerize-loader behavior with a simple promise wrapper when in a testing environment. Any advice would be appreciated.

[developit]

If you export async functions from the module you're workerizing, they are callable without workerize involved:

export async function foo() {
  return 42;
}

import { foo } from 'workerize-loader!./a'
foo()  // Promise<42>

import { foo } from './a'
foo()  // Promise<42>

[wbobeirne]

Yeah, that works like a charm for testing the worker functions themselves. The issue I have is that the function I want to unit test is in a file that includes that worker, or a file that includes that file etc. etc.:

import { foo } from 'workerize-loader!./a'

function async iWantToUnitTestThis() {
  const number = await foo();
  return foo * 2;
}

I hacked around this by using mock-require and mocking the worker for each of those files before running my tests:

function makeWorkerFactory(module) {
  return () => module
}

const workers = ['list', 'of', 'worker.js', 'files']
workers.forEach(worker => {
  const source = require(worker)
  return mock(path, makeWorkerFactory(source))
})

But obviously this isn't ideal.

[developit]

Is the issue that your running your test directly in Node so there is no Worker support?

If so, just drop jsdom-worker in there:
https://github.com/developit/jsdom-worker

[danreeves]

The issue is that workerize-loader changes the shape of the module. You can't use a module that imports a workerized module in jest, for example, because the default export doesn't exist unless you've run it through webpack first.

[serdaroquai]

an alternative way is to tell jest to map the module to a mock implementation

"moduleNameMapper": {
  "workerize-loader!../../worker/some.worker":"<rootDir>/src/worker/some.worker.mock.js"
}

to jest.config.js or if you are using create-react-app to package.json.

...and supply a mock worker at the path you described

module.exports = () => require('./some.worker');

Reference: https://twitter.com/james_k_nelson/status/1175259347422564357

[developit]

I added a variant of that solution to a new testing section in the readme. Cheers!

[paulmelero]

The transform wasn't working for me either (as in #103). This is the error I was getting:

Cannot find module 'workerize-loader!~/core/referenceStyler'

I opted for using the moduleNameMapper as @serdaroquai suggested.

Although I noticed it might be a little bit slow, the test is taking now 5s. Not sure where the problem is yet.

Anyway, thank you for this great library! 🙌 ❤️