added comment explaining a test

theano/gof/tests/test_op.py

@@ -296,11 +296,16 @@ def test_get_debug_values_exc():
 
         try:
             for x_val in op.get_debug_values(x):
+                #this assert catches the case where we
+                #erroneously get a value returned
                 assert False
             raised = False
         except AttributeError:
             raised = True
 
+        #this assert catches the case where we got []
+        #returned, and possibly issued a warning,
+        #rather than raising an exception
         assert raised
 
     finally: