diff --git a/mistral/engine/default_engine.py b/mistral/engine/default_engine.py
index fc15da517..9e8a787a5 100644
--- a/mistral/engine/default_engine.py
+++ b/mistral/engine/default_engine.py
@@ -254,8 +254,8 @@ class DefaultEngine(base.Engine):
                     db_api.update_action_execution_heartbeat(exec_id)
                 except exceptions.DBEntityNotFoundError:
                     LOG.debug(
-                        "Action execution heartbeat update failed. {}"
-                        .format(exec_id),
+                        "Action execution heartbeat update failed. {}",
+                        exec_id,
                         exc_info=True
                     )
                     # Ignore this error and continue with the
diff --git a/mistral/hacking/checks.py b/mistral/hacking/checks.py
index 2eb8ec0b7..3f847eccf 100644
--- a/mistral/hacking/checks.py
+++ b/mistral/hacking/checks.py
@@ -68,24 +68,24 @@ def check_oslo_namespace_imports(logical_line):
         msg = ("O323: '%s' must be used instead of '%s'.") % (
             logical_line.replace('oslo.', 'oslo_'),
             logical_line)
-        yield(0, msg)
+        yield (0, msg)
     elif re.match(oslo_namespace_imports_from_root, logical_line):
         msg = ("O323: '%s' must be used instead of '%s'.") % (
             logical_line.replace('from oslo import ', 'import oslo_'),
             logical_line)
-        yield(0, msg)
+        yield (0, msg)
     elif re.match(oslo_namespace_imports_dot, logical_line):
         msg = ("O323: '%s' must be used instead of '%s'.") % (
             logical_line.replace('import', 'from').replace('.', ' import '),
             logical_line)
-        yield(0, msg)
+        yield (0, msg)
 
 
 @core.flake8ext
 def check_python3_xrange(logical_line):
     if re.search(r"\bxrange\s*\(", logical_line):
-        yield(0, "M327: Do not use xrange(). 'xrange()' is not compatible "
-              "with Python 3. Use range() or range() instead.")
+        yield (0, "M327: Do not use xrange(). 'xrange()' is not compatible "
+               "with Python 3. Use range() or range() instead.")
 
 
 @core.flake8ext
@@ -93,7 +93,7 @@ def check_python3_no_iteritems(logical_line):
     msg = ("M328: Use six.iteritems() instead of dict.iteritems().")
 
     if re.search(r".*\.iteritems\(\)", logical_line):
-        yield(0, msg)
+        yield (0, msg)
 
 
 @core.flake8ext
@@ -101,7 +101,7 @@ def check_python3_no_iterkeys(logical_line):
     msg = ("M329: Use six.iterkeys() instead of dict.iterkeys().")
 
     if re.search(r".*\.iterkeys\(\)", logical_line):
-        yield(0, msg)
+        yield (0, msg)
 
 
 @core.flake8ext
@@ -109,7 +109,7 @@ def check_python3_no_itervalues(logical_line):
     msg = ("M330: Use six.itervalues() instead of dict.itervalues().")
 
     if re.search(r".*\.itervalues\(\)", logical_line):
-        yield(0, msg)
+        yield (0, msg)
 
 
 class BaseASTChecker(ast.NodeVisitor):
diff --git a/mistral/rpc/kombu/kombu_listener.py b/mistral/rpc/kombu/kombu_listener.py
index 41498f16d..94a6e533a 100644
--- a/mistral/rpc/kombu/kombu_listener.py
+++ b/mistral/rpc/kombu/kombu_listener.py
@@ -72,7 +72,7 @@ class KombuRPCListener(ConsumerMixin):
         :param message: the plain amqp kombu.message with additional
             information
         """
-        LOG.debug("Got response: {0}".format(response))
+        LOG.debug("Got response: {}", response)
 
         try:
             message.ack()
@@ -97,7 +97,7 @@ class KombuRPCListener(ConsumerMixin):
             else:
                 LOG.debug(
                     "Got a response, but seems like no process is waiting for "
-                    "it [correlation_id={0}]".format(correlation_id)
+                    "it [correlation_id={}]", correlation_id
                 )
 
     def get_result(self, correlation_id, timeout):
diff --git a/mistral/rpc/kombu/kombu_server.py b/mistral/rpc/kombu/kombu_server.py
index 3ac474255..8e19ba6e6 100644
--- a/mistral/rpc/kombu/kombu_server.py
+++ b/mistral/rpc/kombu/kombu_server.py
@@ -147,8 +147,8 @@ class KombuRPCServer(rpc_base.RPCServer, kombu_base.Base):
                             self.stop()
 
                             LOG.info(
-                                "Server with id='{}' stopped."
-                                .format(self.server_id)
+                                "Server with id='{}' stopped.",
+                                self.server_id
                             )
 
                             return
diff --git a/mistral/services/action_heartbeat_checker.py b/mistral/services/action_heartbeat_checker.py
index 89ebdb337..f1fed2288 100644
--- a/mistral/services/action_heartbeat_checker.py
+++ b/mistral/services/action_heartbeat_checker.py
@@ -51,14 +51,12 @@ def handle_expired_actions():
             CONF.action_heartbeat.batch_size
         )
 
-        LOG.debug("Found {} running and expired actions.".format(
-            len(action_exs))
-        )
+        LOG.debug("Found {} running and expired actions.", len(action_exs))
 
         if action_exs:
             LOG.info(
                 "Actions executions to transit to error, because "
-                "heartbeat wasn't received: {}".format(action_exs)
+                "heartbeat wasn't received: {}", action_exs
             )
 
             for action_ex in action_exs:
@@ -131,7 +129,7 @@ def start():
     LOG.debug(
         "First run of action heartbeat checker, wait before "
         "checking to make sure executors have time to send "
-        "heartbeats. ({} seconds)".format(wait_time)
+        "heartbeats. ({} seconds)", wait_time
     )
 
     global _stopped
diff --git a/mistral/services/maintenance.py b/mistral/services/maintenance.py
index 8d82cf8db..b7f0fd05c 100644
--- a/mistral/services/maintenance.py
+++ b/mistral/services/maintenance.py
@@ -56,8 +56,8 @@ def pause_running_executions(skip_tx=False):
                      db_api.get_workflow_executions(state=states.RUNNING,
                      insecure=True)]
 
-    LOG.info("Number of find workflow executions is {}"
-             .format(len(execution_ids)))
+    LOG.info("Number of find workflow executions is {}",
+             len(execution_ids))
 
     if skip_tx:
         sched = sched_base.get_system_scheduler()
@@ -112,7 +112,7 @@ def _pause_execution(wf_ex_id, project_id, skip_tx=False):
 
     if states.is_running(wf_ex.state):
         workflow_handler.pause_workflow(wf_ex)
-        LOG.info('Execution {} was paused'.format(wf_ex_id))
+        LOG.info('Execution {} was paused', wf_ex_id)
 
 
 def await_pause_executions(skip_tx=False):
@@ -139,9 +139,9 @@ def await_pause_executions(skip_tx=False):
                 db_api.update_maintenance_status(PAUSED)
             return
 
-        LOG.info('The following tasks have RUNNING state: {}'.format([
+        LOG.info('The following tasks have RUNNING state: {}', [
             task.id for task in tasks
-        ]))
+        ])
 
         sched = sched_base.get_system_scheduler()
         job = sched_base.SchedulerJob(
@@ -166,9 +166,9 @@ def await_pause_executions(skip_tx=False):
             if not tasks:
                 return True
 
-            LOG.info('The following tasks have RUNNING state: {}'.format([
+            LOG.info('The following tasks have RUNNING state: {}', [
                 task.id for task in tasks
-            ]))
+            ])
 
             eventlet.sleep(1)
 
@@ -284,6 +284,4 @@ def _resume_execution(wf_ex_id, skip_tx=False):
 
     workflow_handler.resume_workflow(wf_ex)
 
-    LOG.info('The following execution was resumed: {}'.format([
-        wf_ex.id
-    ]))
+    LOG.info('The following execution was resumed: {}', [wf_ex.id])
diff --git a/mistral/tests/unit/api/v2/test_cron_triggers.py b/mistral/tests/unit/api/v2/test_cron_triggers.py
index f824e59b4..b887c48a8 100644
--- a/mistral/tests/unit/api/v2/test_cron_triggers.py
+++ b/mistral/tests/unit/api/v2/test_cron_triggers.py
@@ -110,7 +110,7 @@ class TestCronTriggerController(base.APITest):
         resp = self.app.get('/v2/cron_triggers/my_cron_trigger')
 
         self.assertEqual(200, resp.status_int)
-        self.assertTrue('project_id' in resp.json)
+        self.assertIn('project_id', resp.json)
 
     @mock.patch.object(db_api, "get_cron_trigger", MOCK_NOT_FOUND)
     def test_get_not_found(self):
diff --git a/mistral/tests/unit/api/v2/test_executions.py b/mistral/tests/unit/api/v2/test_executions.py
index 101f930f9..a54c14e17 100644
--- a/mistral/tests/unit/api/v2/test_executions.py
+++ b/mistral/tests/unit/api/v2/test_executions.py
@@ -224,7 +224,7 @@ class TestExecutionsController(base.APITest):
         resp = self.app.get('/v2/executions/123', expect_errors=True)
 
         self.assertEqual(200, resp.status_int)
-        self.assertTrue('project_id' in resp.json)
+        self.assertIn('project_id', resp.json)
 
     @mock.patch.object(
         db_api,
diff --git a/mistral/tests/unit/api/v2/test_tasks.py b/mistral/tests/unit/api/v2/test_tasks.py
index 615cf1bc3..9620f0af5 100644
--- a/mistral/tests/unit/api/v2/test_tasks.py
+++ b/mistral/tests/unit/api/v2/test_tasks.py
@@ -242,7 +242,7 @@ class TestTasksController(base.APITest):
         resp = self.app.get('/v2/tasks/123')
 
         self.assertEqual(200, resp.status_int)
-        self.assertTrue('project_id' in resp.json)
+        self.assertIn('project_id', resp.json)
 
     @mock.patch.object(db_api, 'get_task_executions', MOCK_EMPTY)
     def test_get_all_empty(self):
diff --git a/mistral/tests/unit/api/v2/test_workbooks.py b/mistral/tests/unit/api/v2/test_workbooks.py
index ed550affb..930815964 100644
--- a/mistral/tests/unit/api/v2/test_workbooks.py
+++ b/mistral/tests/unit/api/v2/test_workbooks.py
@@ -213,7 +213,7 @@ class TestWorkbooksController(base.APITest):
         resp = self.app.get('/v2/workbooks/123')
 
         self.assertEqual(200, resp.status_int)
-        self.assertTrue('project_id' in resp.json)
+        self.assertIn('project_id', resp.json)
 
     @mock.patch.object(workbooks, "update_workbook_v2", MOCK_UPDATED_WORKBOOK)
     def test_put(self):
diff --git a/mistral/workflow/base.py b/mistral/workflow/base.py
index 8e182f7ed..898db724b 100644
--- a/mistral/workflow/base.py
+++ b/mistral/workflow/base.py
@@ -232,7 +232,7 @@ class WorkflowController(object):
 
     @abc.abstractmethod
     def evaluate_workflow_final_context(self):
-        """Evaluates final workflow context assuming that workflow has finished.
+        """Evaluates final workflow context after workflow has finished.
 
         :return: Final workflow context.
         """
diff --git a/requirements.txt b/requirements.txt
index e59b3da4b..8f7d557d1 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,7 +1,3 @@
-# The order of packages is significant, because pip processes them in the order
-# of appearance. Changing the order has an impact on the overall integration
-# process, which may cause wedges in the gate later.
-
 alembic>=0.9.6 # MIT
 croniter>=0.3.4 # MIT License
 cachetools>=2.0.0 # MIT License
diff --git a/test-requirements.txt b/test-requirements.txt
index 948abceef..1f8f8b8b3 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -1,7 +1,4 @@
-# The order of packages is significant, because pip processes them in the order
-# of appearance. Changing the order has an impact on the overall integration
-# process, which may cause wedges in the gate later.
-hacking>=3.0.1,<3.1.0 # Apache-2.0
+hacking>=6.1.0,<6.2.0 # Apache-2.0
 
 coverage!=4.4,>=4.0 # Apache-2.0
 doc8>=0.8.1 # Apache-2.0