possible to replace subset of exports from module?

sample.js

export {a, b}

function a() {
  return b()
}

function b() {
  return 'b'
}

want to replace b() but preserve a()...

td.test.js

import test from 'ava'
import * as td from 'testdouble'
// import {a} from './sample.js'

let mock

test.beforeEach(async () => {
  // unclear how to use second parameter here, is this a potential solution?
  // or is the ask not supported and would need to place `a` and `b` in separate files?
  //
  mock = await td.replaceEsm('./sample.js')
})

test.afterEach(async () => {
  td.reset()
})

test('a', (t) => {
  td.when(mock.b()).thenResolve('bee')
  t.is(mock.a(), 'bee')
})

test('b', (t) => {
  td.when(mock.b()).thenReturn('be')
  t.is(mock.b(), 'be')
})

Start with td.test.js and the replaceEsm entry point to determine whether partial export replacement is supported. Use sample.js as the fixture and make the test demonstrate preserving a while replacing b; done means both assertions pass without moving the functions.