msw/test/browser/msw-api/setup-worker/start/find-worker.mocks.ts

import { http } from 'msw'
import { setupWorker } from 'msw/browser'

const worker = setupWorker(
  http.get('/user', () => {
    return new Response()
  }),
)

Object.assign(window, {
  msw: {
    registration: worker
      .start({
        // This is the default matching behavior if left unspecified.
        findWorker(scriptURL, mockServiceWorkerUrl) {
          return scriptURL === mockServiceWorkerUrl
        },
      })
      .then((registration) => {
        console.log('Registration Promise resolved', registration)
        return registration?.constructor.name
      }),
  },
})