add comments.empty

isso/controllers/comments.py

@@ -237,6 +237,10 @@ class Controller(object):
 
         return obj
 
+    def empty(self):
+        return self.db.engine.execute(
+            select([func.count(self.db.comments)])).fetchone()[0] == 0
+
     def count(self, *threads):
         """Retrieve comment count for :param threads:
         """

isso/tests/controllers/test_comments.py

@@ -176,6 +176,11 @@ class TestController(unittest.TestCase):
         self.controller.delete(c2.id)
         self.assertIsNone(self.controller.get(p.id))
 
+    def test_empty(self):
+        self.assertTrue(self.controller.empty())
+        self.controller.new(IP, TH, dict(text="..."))
+        self.assertFalse(self.controller.empty())
+
     def test_count(self):
         threads = [Thread(0, "a"), None, Thread(1, "c")]
         counter = [1, 0, 2]