diff --git a/force_bdss/cli/tests/test_execution.py b/force_bdss/cli/tests/test_execution.py
index 50cf18014cd566bbfd97a97e559a495f603caff5..d427e154134ef6e55f1688dbf09a08d89e2f5808 100644
--- a/force_bdss/cli/tests/test_execution.py
+++ b/force_bdss/cli/tests/test_execution.py
@@ -3,6 +3,8 @@ import subprocess
 import os
 from contextlib import contextmanager
 
+import six
+
 from force_bdss.tests import fixtures
 
 
@@ -43,16 +45,16 @@ class TestExecution(unittest.TestCase):
             with self.assertRaises(subprocess.CalledProcessError):
                 subprocess.check_call(
                     ["force_bdss", "test_csv_v2.json"],
-                    stdout=subprocess.DEVNULL,
-                    stderr=subprocess.DEVNULL)
+                    stdout=os.devnull,
+                    stderr=os.devnull)
 
     def test_corrupted_file_input(self):
         with cd(fixtures.dirpath()):
             with self.assertRaises(subprocess.CalledProcessError):
                 subprocess.check_call(
                     ["force_bdss", "test_csv_corrupted.json"],
-                    stdout=subprocess.DEVNULL,
-                    stderr=subprocess.DEVNULL)
+                    stdout=os.devnull,
+                    stderr=os.devnull)
 
 
 if __name__ == '__main__':
diff --git a/force_bdss/tests/test_core_evaluation_driver.py b/force_bdss/tests/test_core_evaluation_driver.py
index 141c8a3f5d6e2f1eca92c472cb77bd9ed4b0c39b..a6084e73294e123a6570e3a2086b08cdb948729d 100644
--- a/force_bdss/tests/test_core_evaluation_driver.py
+++ b/force_bdss/tests/test_core_evaluation_driver.py
@@ -1,6 +1,7 @@
 import unittest
 
 import testfixtures
+import six
 
 from force_bdss.tests.probe_classes.factory_registry_plugin import \
     ProbeFactoryRegistryPlugin
@@ -49,7 +50,8 @@ class TestCoreEvaluationDriver(unittest.TestCase):
         driver = CoreEvaluationDriver(
             application=self.mock_application)
         with testfixtures.LogCapture():
-            with self.assertRaisesRegex(
+            with six.assertRaisesRegex(
+                    self,
                     RuntimeError,
                     "The number of data values returned by the MCO"):
                 driver.application_started()
@@ -66,7 +68,8 @@ class TestCoreEvaluationDriver(unittest.TestCase):
         driver = CoreEvaluationDriver(
             application=self.mock_application)
         with testfixtures.LogCapture():
-            with self.assertRaisesRegex(
+            with six.assertRaisesRegex(
+                    self,
                     RuntimeError,
                     "The number of data values \(1 values\)"
                     " returned by 'test_data_source' does not match"
@@ -87,7 +90,8 @@ class TestCoreEvaluationDriver(unittest.TestCase):
             application=self.mock_application,
         )
         with testfixtures.LogCapture():
-            with self.assertRaisesRegex(
+            with six.assertRaisesRegex(
+                    self,
                     RuntimeError,
                     "The number of data values \(1 values\)"
                     " returned by 'test_data_source' does not match"
@@ -107,7 +111,8 @@ class TestCoreEvaluationDriver(unittest.TestCase):
             application=self.mock_application,
         )
         with testfixtures.LogCapture():
-            with self.assertRaisesRegex(
+            with six.assertRaisesRegex(
+                    self,
                     RuntimeError,
                     "The number of data values \(1 values\)"
                     " returned by 'test_kpi_calculator' does not match"
@@ -130,7 +135,8 @@ class TestCoreEvaluationDriver(unittest.TestCase):
         )
 
         with testfixtures.LogCapture():
-            with self.assertRaisesRegex(
+            with six.assertRaisesRegex(
+                    self,
                     RuntimeError,
                     "The number of data values \(1 values\)"
                     " returned by 'test_kpi_calculator' does not match"
@@ -164,7 +170,8 @@ class TestCoreEvaluationDriver(unittest.TestCase):
         )
 
         with testfixtures.LogCapture():
-            with self.assertRaisesRegex(
+            with six.assertRaisesRegex(
+                    self,
                     RuntimeError,
                     "The length of the slots is not equal to the length of"
                     " the slot map"):
@@ -177,7 +184,8 @@ class TestCoreEvaluationDriver(unittest.TestCase):
         )
 
         with testfixtures.LogCapture():
-            with self.assertRaisesRegex(
+            with six.assertRaisesRegex(
+                    self,
                     RuntimeError,
                     "Unable to find requested name 'blap' in available"
                     " data values."):