FeatureContext.php

<?php

  /**
   * @When I switch to the frame by selector "[title=:arg1]"
   */
  public function switchToIFrameFromSelector($iframeSelector) {
    $function = <<<JS
    (function(){var iframe = document.querySelector("$iframeSelector");iframe.name = "iframeToSwitchTo";})()
JS;
    try {
      $this->getSession()->executeScript($function);
    }catch (Exception $e){
      throw new \Exception("Element $iframeSelector was NOT found.".PHP_EOL . $e->getMessage());
    }
    $this->getSession()->getDriver()->switchToIFrame("iframeToSwitchTo");
  }

  /**
   * @When /^(?:|I )fill in the iframe field with "(?P<value>(?:[^"]|\\")*)"$/
   */
  public function iFillInTheIframeField($value)
  {
    $this->spin(function (FeatureContext $context) use ($value) {
      try {
        $session = $this->getSession();
        $field = $this->getSession()->getPage()->find('xpath', '//input');

        if (!$field) {
          throw new \Exception(sprintf('No input found on the page %s.', $session->getCurrentUrl()));
        }
        $field->setValue($value);
        return TRUE;
      }
      catch (\Exception $e) {
        return FALSE;
      }
    });
  }

harhar.features

    # Braintree
    And I wait
    When I switch to the frame "braintree-hosted-field-number"
      Then I fill in the iframe field with "5555555555554444"
      Then I switch out of all frames
    When I switch to the frame "braintree-hosted-field-expirationMonth"
      Then I fill in the iframe field with "03"
      Then I switch out of all frames
    When I switch to the frame "braintree-hosted-field-expirationYear"
      Then I fill in the iframe field with "20"
      Then I switch out of all frames
    When I switch to the frame "braintree-hosted-field-cvv"
      Then I fill in the iframe field with "123"
    Then I switch out of all frames
    # Back to Drupal
    When I fill in the following:
      | First name     | Joseph         |
      | Last name      | Schlitz        |
      | Street address | 2929 Browns Ln |
      | City           | Jonesboro      |
      | State          | AR             |
      | Zip code       | 72401          |
    And I press "Continue to review"