Not possible to read value returned from Chromy

[VladimirPittner]

Hi,
according to Chromy documentation, something like this should be possible:

const Chromy = require('chromy')

async function main () {
  let chromy = new Chromy()
  await chromy.goto('http://example.com/')
  const result = await chromy.evaluate(() => {
          return document.querySelectorAll('*').length
        })
  console.log(result)
  await chromy.close()
}

main()

Therefor I would expect something like this should be possible within BackstopJs:

async function myFunction(chromy, scenario, vp) {


    const result = await chromy.evaluate(() => {
        return document.querySelectorAll('*').length
    })
    console.log(result)

};

module.exports = myFunction;

But I am getting this error:

(node:15120) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 2): Error: 'then' is not defined on a target object.
(node:15120) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Any idea what I might doing wrong?