diff --git a/tests/async/test_simple_client.py b/tests/async/test_simple_client.py
index f8996bd..08b2ea6 100644
--- a/tests/async/test_simple_client.py
+++ b/tests/async/test_simple_client.py
@@ -32,7 +32,7 @@ class TestAsyncAsyncSimpleClient(unittest.TestCase):
                 'url', headers='h', auth='a', transports='t',
                 namespaces=['n'], socketio_path='s', wait_timeout='w')
             mock_client().event.call_count == 3
-            mock_client().on.called_once_with('*')
+            mock_client().on.assert_called_once_with('*', namespace='n')
             assert client.namespace == 'n'
             assert not client.input_event.is_set()
 
@@ -52,7 +52,8 @@ class TestAsyncAsyncSimpleClient(unittest.TestCase):
                         'url', headers='h', auth='a', transports='t',
                         namespaces=['n'], socketio_path='s', wait_timeout='w')
                     mock_client().event.call_count == 3
-                    mock_client().on.called_once_with('*')
+                    mock_client().on.assert_called_once_with(
+                        '*', namespace='n')
                     assert client.namespace == 'n'
                     assert not client.input_event.is_set()
 
@@ -85,7 +86,7 @@ class TestAsyncAsyncSimpleClient(unittest.TestCase):
         client.connected = True
 
         _run(client.emit('foo', 'bar'))
-        assert client.client.emit.mock.called_once_with('foo', 'bar',
+        client.client.emit.mock.assert_called_once_with('foo', 'bar',
                                                         namespace='/ns')
 
     def test_emit_disconnected(self):
@@ -116,9 +117,8 @@ class TestAsyncAsyncSimpleClient(unittest.TestCase):
         client.connected = True
 
         assert _run(client.call('foo', 'bar')) == 'result'
-        assert client.client.call.mock.called_once_with('foo', 'bar',
-                                                        namespace='/ns',
-                                                        timeout=60)
+        client.client.call.mock.assert_called_once_with(
+            'foo', 'bar', namespace='/ns', timeout=60)
 
     def test_call_disconnected(self):
         client = AsyncSimpleClient()
diff --git a/tests/common/test_simple_client.py b/tests/common/test_simple_client.py
index 4069042..3b9f983 100644
--- a/tests/common/test_simple_client.py
+++ b/tests/common/test_simple_client.py
@@ -25,7 +25,7 @@ class TestSimpleClient(unittest.TestCase):
                 'url', headers='h', auth='a', transports='t',
                 namespaces=['n'], socketio_path='s', wait_timeout='w')
             mock_client().event.call_count == 3
-            mock_client().on.called_once_with('*')
+            mock_client().on.assert_called_once_with('*', namespace='n')
             assert client.namespace == 'n'
             assert not client.input_event.is_set()
 
@@ -41,7 +41,7 @@ class TestSimpleClient(unittest.TestCase):
                     'url', headers='h', auth='a', transports='t',
                     namespaces=['n'], socketio_path='s', wait_timeout='w')
                 mock_client().event.call_count == 3
-                mock_client().on.called_once_with('*')
+                mock_client().on.assert_called_once_with('*', namespace='n')
                 assert client.namespace == 'n'
                 assert not client.input_event.is_set()
 
@@ -71,7 +71,7 @@ class TestSimpleClient(unittest.TestCase):
         client.connected = True
 
         client.emit('foo', 'bar')
-        assert client.client.emit.called_once_with('foo', 'bar',
+        client.client.emit.assert_called_once_with('foo', 'bar',
                                                    namespace='/ns')
 
     def test_emit_disconnected(self):
@@ -100,8 +100,8 @@ class TestSimpleClient(unittest.TestCase):
         client.connected = True
 
         assert client.call('foo', 'bar') == 'result'
-        client.client.call.called_once_with('foo', 'bar', namespace='/ns',
-                                            timeout=60)
+        client.client.call.assert_called_once_with('foo', 'bar',
+                                                   namespace='/ns', timeout=60)
 
     def test_call_disconnected(self):
         client = SimpleClient()