Jest virtual mock: how do I troubleshoot this failure?

So I have this import statement for a module that is only available when running on the jvm's nashorn runtime in the module i'm trying to test using jest 25.1 running on node 11.1.0:

import RequestBuilder from 'nashorn-js/request_builder'

...and after the other lines in the import block, this:

const request = RequestBuilder.create('some-string')
.sendTo('some-other-string')
.withAction('yet-another-string')
.getResultWith( consumer => consumer.result( consumer.message().body() ) )

export const functionA = () => {...} // uses 'request' variable

export const functionB = () => {...} // uses 'request' variable

In the corresponding .spec file, I have this virtual mock setup:

const mockGetResultWith = {
  getResultWith: jest.fn()
}
const mockWithAction = {
  withAction: jest.fn().mockImplementation(() => mockGetResultWith)
}
const mockSendTo = {
  sendTo: jest.fn().mockImplementation(() => mockWithAction)
}
const mockBuilder = {
  create: jest.fn().mockImplementation(() => mockSendTo)
}
jest.mock(
  'nashorn-js/request_builder',
  () => mockBuilder,
  { virtual: true }
)

require('nashorn-js/request_builder')

import { functionA, functionB } from './module-under-test'

I have been trying unsuccessfully to get past this failure from jest:

● Test suite failed to run

    TypeError: Cannot read property 'create' of undefined

      35 | }
      36 | 
    > 37 | const verify = RequestBuilder.create('some-string')
         |                               ^
      38 | .sendTo('some-other-string')
      39 | .withAction('yet-another-string')
      40 | .getResultWith( consumer => consumer.result( consumer.message().body() ) )

I've tried all kinds of different mock structures, using require vs import, etc, but haven't found the magic bullet.

As near as I can tell, it does not appear that the RequestBuilder import statement is even invoking the virtual mock. Or at least, if I add console.log() statements to the virtual mock factory function, I never see those log messages in the output.

Anybody have any idea what I'm missing or what else to try? I have pretty much the same pattern in use in other parts of the code, where this setup works, but for some mystical reason with this module, I can't get the virtual mock working. Any help is greatly appreciated.