To use a collection with periods in its name, quote it with braces:
<?php
$m = new MongoClient();
$cursor = $m->test->{'test.test'}->find();
## equivalent to the following:
#$db = $m->test;
#$collection = $db->{'test.test'};
#$cursor = $collection->find();
foreach ($cursor as $doc) {
print_r($doc);
?>