diff --git a/neutron/tests/functional/test_server.py b/neutron/tests/functional/test_server.py
index 41bbedda09b..fc8b5c7b610 100644
--- a/neutron/tests/functional/test_server.py
+++ b/neutron/tests/functional/test_server.py
@@ -23,6 +23,7 @@ import httplib2
 import mock
 from neutron_lib import worker as neutron_worker
 from oslo_config import cfg
+from oslo_log import log
 import psutil
 import six
 
@@ -33,6 +34,8 @@ from neutron.tests.functional import base
 from neutron import wsgi
 
 
+LOG = log.getLogger(__name__)
+
 CONF = cfg.CONF
 
 # Those messages will be written to temporary file each time
@@ -156,12 +159,19 @@ class TestNeutronServer(base.BaseLoggingTestCase):
         # Wait for temp file to be created and its size reaching the expected
         # value
         expected_size = len(expected_msg)
-        condition = lambda: (os.path.isfile(self.temp_file) and
-                             os.stat(self.temp_file).st_size ==
-                             expected_size)
+
+        def is_temp_file_ok():
+            LOG.debug("Checking file %s", self.temp_file)
+            if not os.path.isfile(self.temp_file):
+                LOG.debug("File %s not exists.", self.temp_file)
+                return False
+            temp_file_size = os.stat(self.temp_file).st_size
+            LOG.debug("Size of file %s is %s. Expected size: %s",
+                      self.temp_file, temp_file_size, expected_size)
+            return temp_file_size == expected_size
 
         try:
-            utils.wait_until_true(condition, timeout=5, sleep=1)
+            utils.wait_until_true(is_temp_file_ok, timeout=5, sleep=1)
         except utils.TimerTimeout:
             if not os.path.isfile(self.temp_file):
                 raise RuntimeError(