Checks the matching requirements for Test.
Array of errors containing a list of unmet requirements.
Overrides TestBase::checkRequirements
protected function checkRequirements() {
  $gd_available = FALSE;
  if ($check = get_extension_funcs('gd')) {
    if (in_array('imagegd2', $check)) {
      // GD2 support is available.
      $gd_available = TRUE;
    }
  }
  if (!$gd_available) {
    return array(
      'Image manipulations for the GD toolkit cannot run because the GD toolkit is not available.',
    );
  }
  return parent::checkRequirements();
}