diff --git a/test/test_protocol.py b/test/test_protocol.py
index 1e7440b..7846b32 100644
--- a/test/test_protocol.py
+++ b/test/test_protocol.py
@@ -68,6 +68,6 @@ class ProtocolTest(unittest.TestCase):
 
         # 2nd call of keep_alive should close the transport
         self.protocol.keep_alive()
-        assert mock_transport.close.called_once()
+        mock_transport.close.assert_called_once()
 
         self.protocol.connection_lost(None)
diff --git a/tox.ini b/tox.ini
index 533aa72..59d57e7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,6 +6,7 @@ deps=
   pytest-asyncio
   pytest-mock
   dlms_cosem
+  setuptools
 commands=
   py.test --cov=dsmr_parser test {posargs}
   pylama dsmr_parser test