Pass if a link with the specified label is found, and optional with the specified index.
$label: Text between the anchor tags.
$index: Link position counting from zero.
$message: Message to display.
$group: The group this message belongs to, defaults to 'Other'.
TRUE if the assertion succeeded, FALSE otherwise.
protected function assertLink($label, $index = 0, $message = '', $group = 'Other') {
$links = $this
->xpath('//a[normalize-space(text())=:label]', array(
':label' => $label,
));
$message = $message ? $message : t('Link with label %label found.', array(
'%label' => $label,
));
return $this
->assert(isset($links[$index]), $message, $group);
}