Support MongoClient in MongoDBHandler

tests/Monolog/Handler/MongoDBHandlerTest.php

@@ -16,6 +16,14 @@ use Monolog\Logger;
 
 class MongoDBHandlerTest extends TestCase
 {
+    /**
+     * @expectedException InvalidArgumentException
+     */
+    public function testConstructorShouldThrowExceptionForInvalidMongo()
+    {
+        new MongoDBHandler(new \stdClass(), 'DB', 'Collection');
+    }
+
     public function testHandle()
     {
         $mongo = $this->getMock('Mongo', array('selectCollection'));