function createFile(options) {
  const children = options.children || ''
  const file = new VFile()

  if (typeof children === 'string') {
    file.value = children
  } else {
    unreachable(
      'Unexpected value `' +
        children +
        '` for `children` prop, expected `string`'
    )
  }

  return file
}
Set up the virtual file.

@param {Readonly<Options>} options
  Props.
@returns {VFile}
  Result.