Enable running unit tests in py37 environment

Until now no unit tests have been executed in py37 environment. This
change fixes tox configuration to enable running these tests.

It also fixes two unit tests to handle PEP479 being enabled for all code
in Python 3.7 [1, 2].

[1] https://docs.python.org/3/whatsnew/3.7.html#changes-in-python-behavior
[2] https://stackoverflow.com/questions/51700960/runtimeerror-generator-raised-stopiteration-every-time-i-try-to-run-app

Change-Id: I7fcf30d848efb8dc4cc6ca19056868aa6127cf60

monasca_common/tests/test_confluent_kafka.py

@@ -162,8 +162,12 @@ class TestConfluentKafkaConsumer(base.BaseTestCase):
             m.set_value("message{}".format(i))
             messages.append(m)
         self.consumer._consumer.poll.side_effect = messages
-        for index, message in enumerate(self.consumer):
-            self.assertEqual(message, messages[index])
+        try:
+            for index, message in enumerate(self.consumer):
+                self.assertEqual(message, messages[index])
+        except RuntimeError as re:
+            if 'generator raised StopIteration' in str(re):
+                pass
 
     @mock.patch('confluent_kafka.Message')
     @mock.patch('confluent_kafka.KafkaError')

monasca_common/tests/test_kafka.py

@@ -173,6 +173,10 @@ class TestKafkaConsumer(base.BaseTestCase):
         mock_set_partitioner.return_value.acquired = True
         mock_set_partitioner.return_value.__iter__.return_value = [1]
 
-        list(self.monasca_kafka_consumer)
+        try:
+            list(self.monasca_kafka_consumer)
+        except RuntimeError as re:
+            if 'generator raised StopIteration' in str(re):
+                pass
 
         self.consumer.seek.assert_called_once_with(0, 0)

tox.ini

@@ -34,6 +34,15 @@ commands =
   {[testenv]commands}
   stestr run --blacklist-file {env:BLACKLIST_FILE} {posargs}
 
+[testenv:py37]
+basepython = python3.7
+setenv =
+  {[testenv]setenv}
+  BLACKLIST_FILE={toxinidir}/test-blacklist-py3.txt
+commands =
+  {[testenv]commands}
+  stestr run --blacklist-file {env:BLACKLIST_FILE} {posargs}
+
 [testenv:cover]
 setenv =
     PYTHON=coverage run --source monasca_common --parallel-mode