Behat Step to select an autocomplete suggestion

gistfile1.php

<?php

use Behat\Mink\Extension\ElementNotFoundException;
use Drupal\DrupalExtension\Context\DrupalContext;

class FeatureContext extends DrupalContext {

  /**
   * @When I select the first autocomplete option for :prefix on the :field field
   */
  public function iSelectFirstAutocomplete($prefix, $field) {
    $field = $this->fixStepArgument($field);
    $session = $this->getSession();
    $page = $session->getPage();
    $element = $page->findField($field);
    if (!$element) {
      throw new ElementNotFoundException($session, NULL, 'named', $field);
    }

    $page->fillField($field, $prefix);

    $xpath = $element->getXpath();
    $driver = $session->getDriver();
    $prefix = $this->fixStepArgument($prefix);

    $chars = str_split($prefix);

    $last_char = array_pop($chars);

    // autocomplete.js uses key down/up events directly.
    $driver->keyDown($xpath, 8);
    $driver->keyUp($xpath, 8);

    $driver->keyDown($xpath, $last_char);
    $driver->keyUp($xpath, $last_char);

    // Wait for AJAX to finish.
    $this->getSession()->wait(500, '(typeof(jQuery)=="undefined" || (0 === jQuery.active && 0 === jQuery(\':animated\').length))');

    // Press the down arrow to select the first option.
    $driver->keyDown($xpath, 40);
    $driver->keyUp($xpath, 40);

    // Press the Enter key to confirm selection, copying the value into the field.
    $driver->keyDown($xpath, 13);
    $driver->keyUp($xpath, 13);

    // Wait for AJAX to finish.
    $this->getSession()->wait(500, '(typeof(jQuery)=="undefined" || (0 === jQuery.active && 0 === jQuery(\':animated\').length))');
  }

}
?>