Behat Step to select the first autocomplete suggestion

d8-behat-iSelectFirstAutocomplete.php

<?php

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

class FeatureContext extends DrupalContext {

  /**
   * Gives us acess to the other contexts so we can access their properties.
   *
   * @BeforeScenario
   */
  public function gatherContexts(BeforeScenarioScope $scope) {

    $environment = $scope->getEnvironment();

    $this->contexts['drupal'] = $environment->getContext('Drupal\DrupalExtension\Context\DrupalContext');
    $this->contexts['mink'] = $environment->getContext('Drupal\DrupalExtension\Context\MinkContext');
  }

  /**
   * @When I select the first autocomplete option for :prefix on the :field field
   */
  public function iSelectFirstAutocomplete($prefix, $field) {

    $session = $this->getSession();
    $element = $session->getPage()->findField($field);
    if (empty($element)) {

      throw new ElementNotFoundException($session, NULL, 'named', $field);
    }

    $element->setValue($prefix);
    $element->focus();

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

    // autocomplete.js uses key down/up events directly.
    // Press the down arrow to open the autocomplete options.
    $driver->keyDown($xpath, 40);
    $driver->keyUp($xpath, 40);

    $this->contexts['mink']->iWaitForAjaxToFinish();

    // 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);

    $this->contexts['mink']->iWaitForAjaxToFinish();
  }
}