Returns the first element found from Mink's NodeElement::findAll() request.

mink-step-helper-elementselectfirst.php

/**
 * Select the first CSS element returned by findAll query.
 *
 * @param string $selector.
 *   CSS selector.
 *
 * @return NodeElement
 *   Or throws error if unable to locate.
 */
protected function elementSelectFirst($selector)
{
    $session = $this->getSession();
    $elements = $session->getPage()->findAll('css', $selector);
    if (is_array($elements)) {
        $element = array_shift($elements);
    }
    if (null === $element) {
        throw new \InvalidArgumentException(sprintf('Could not locate css selector: "%s"', $selector));
    }
      return $element;
}