diff --git a/app/src/gen3plus/solarman_v5.py b/app/src/gen3plus/solarman_v5.py
index 0cbdfab..94089f3 100644
--- a/app/src/gen3plus/solarman_v5.py
+++ b/app/src/gen3plus/solarman_v5.py
@@ -172,7 +172,7 @@ class SolarmanV5(Message):
         self.db.set_db_def_value(Register.POLLING_INTERVAL,
                                  self.mb_timeout)
         self.db.set_db_def_value(Register.HEARTBEAT_INTERVAL,
-                                 120)  # fixme
+                                 120)
         self.new_data['controller'] = True
 
         self.state = State.up
diff --git a/app/src/inverter.py b/app/src/inverter.py
index cf20c96..7f3914f 100644
--- a/app/src/inverter.py
+++ b/app/src/inverter.py
@@ -1,11 +1,15 @@
 import asyncio
 import logging
 import json
-from config import Config
-from mqtt import Mqtt
-from infos import Infos
+if __name__ == "app.src.inverter":
+    from app.src.config import Config
+    from app.src.mqtt import Mqtt
+    from app.src.infos import Infos
+else:  # pragma: no cover
+    from config import Config
+    from mqtt import Mqtt
+    from infos import Infos
 
-# logger = logging.getLogger('conn')
 logger_mqtt = logging.getLogger('mqtt')
 
 
@@ -24,6 +28,7 @@ class Inverter():
         cls.proxy_unique_id = ha['proxy_unique_id']
 
         # call Mqtt singleton to establisch the connection to the mqtt broker
+        print('call Mqtt.init')
         cls.mqtt = Mqtt(cls._cb_mqtt_is_up)
 
         # register all counters which should be reset at midnight.
@@ -72,7 +77,7 @@ class Inverter():
             Infos.new_stat_data[key] = False
 
     @classmethod
-    def class_close(cls, loop) -> None:
+    def class_close(cls, loop) -> None:   # pragma: no cover
         logging.debug('Inverter.class_close')
         logging.info('Close MQTT Task')
         loop.run_until_complete(cls.mqtt.close())
diff --git a/app/tests/test_inverter.py b/app/tests/test_inverter.py
new file mode 100644
index 0000000..40b23bf
--- /dev/null
+++ b/app/tests/test_inverter.py
@@ -0,0 +1,90 @@
+# test_with_pytest.py
+import pytest
+import asyncio
+import aiomqtt
+import logging
+
+from mock import patch, Mock
+from app.src.singleton import Singleton
+from app.src.inverter import Inverter
+from app.src.mqtt import Mqtt
+from app.src.gen3plus.solarman_v5 import SolarmanV5
+from app.src.config import Config
+
+
+pytest_plugins = ('pytest_asyncio',)
+
+
+@pytest.fixture(scope="module", autouse=True)
+def module_init():
+    def new_init(cls, cb_mqtt_is_up):
+        cb_mqtt_is_up()
+
+    Singleton._instances.clear()
+    with patch.object(Mqtt, '__init__', new_init):
+        yield
+
+@pytest.fixture(scope="module")
+def test_port():
+    return 1883
+
+@pytest.fixture(scope="module")
+def test_hostname():
+    # if getenv("GITHUB_ACTIONS") == "true":
+    #     return 'mqtt'
+    # else:
+        return 'test.mosquitto.org'
+
+@pytest.fixture
+def config_conn(test_hostname, test_port):
+    Config.act_config = {
+                        'mqtt':{
+                            'host': test_hostname,
+                            'port': test_port,
+                            'user': '',
+                            'passwd': ''
+                        },
+                        'ha':{
+                            'auto_conf_prefix': 'homeassistant',
+                            'discovery_prefix': 'homeassistant', 
+                            'entity_prefix': 'tsun',
+                            'proxy_node_id': 'test_1',
+                            'proxy_unique_id': ''
+                        },
+                        'inverters': {
+                            'allow_all': True,
+                            "R170000000000001":{
+                                'node_id': 'inv_1'
+                            }
+                        }
+    }
+
+@pytest.mark.asyncio
+async def test_inverter_cb(config_conn):
+    _ = config_conn
+
+    with patch.object(Inverter, '_cb_mqtt_is_up', wraps=Inverter._cb_mqtt_is_up) as spy:
+        print('call Inverter.class_init')
+        Inverter.class_init()
+        assert 'homeassistant/' == Inverter.discovery_prfx
+        assert 'tsun/' == Inverter.entity_prfx
+        assert 'test_1/' == Inverter.proxy_node_id
+        spy.assert_called_once()
+
+@pytest.mark.asyncio
+async def test_mqtt_is_up(config_conn):
+    _ = config_conn
+
+    with patch.object(Mqtt, 'publish') as spy:
+        Inverter.class_init()
+        await Inverter._cb_mqtt_is_up()
+        spy.assert_called()
+
+@pytest.mark.asyncio
+async def test_mqtt_proxy_statt_invalid(config_conn):
+    _ = config_conn
+
+    with patch.object(Mqtt, 'publish') as spy:
+        Inverter.class_init()
+        await Inverter._async_publ_mqtt_proxy_stat('InValId_kEy')
+        spy.assert_not_called()
diff --git a/app/tests/test_mqtt.py b/app/tests/test_mqtt.py
index 7dea973..1d7c5dd 100644
--- a/app/tests/test_mqtt.py
+++ b/app/tests/test_mqtt.py
@@ -5,6 +5,7 @@ import aiomqtt
 import logging
 
 from mock import patch, Mock
+from app.src.singleton import Singleton
 from app.src.mqtt import Mqtt
 from app.src.modbus import Modbus
 from app.src.gen3plus.solarman_v5 import SolarmanV5
@@ -13,7 +14,10 @@ from app.src.config import Config
 
 pytest_plugins = ('pytest_asyncio',)
 
-
+@pytest.fixture(scope="module", autouse=True)
+def module_init():
+    Singleton._instances.clear()
+    yield
 
 @pytest.fixture(scope="module")
 def test_port():
diff --git a/app/tests/test_singleton.py b/app/tests/test_singleton.py
index 2ea82eb..d645e08 100644
--- a/app/tests/test_singleton.py
+++ b/app/tests/test_singleton.py
@@ -7,6 +7,7 @@ class Test(metaclass=Singleton):
         pass  # is a dummy test class
 
 def test_singleton_metaclass():
+    Singleton._instances.clear()
     a = Test()
     assert 1 == len(Singleton._instances)
     b = Test()
diff --git a/app/tests/test_talent.py b/app/tests/test_talent.py
index 62df532..13f462e 100644
--- a/app/tests/test_talent.py
+++ b/app/tests/test_talent.py
@@ -1150,7 +1150,7 @@ def test_msg_ota_invalid(config_tsun_inv1, msg_ota_invalid):
     m.close()
 
 def test_msg_unknown(config_tsun_inv1, msg_unknown):
-    config_tsun_inv1
+    _ = config_tsun_inv1
     m = MemoryStream(msg_unknown, (0,), False)
     m.db.stat['proxy']['Unknown_Msg'] = 0
     m.read()         # read complete msg, and dispatch msg
diff --git a/system_tests/test_tcp_socket.py b/system_tests/test_tcp_socket.py
index 00ec70f..795184d 100644
--- a/system_tests/test_tcp_socket.py
+++ b/system_tests/test_tcp_socket.py
@@ -138,9 +138,9 @@ def tempClientConnection():
 
 def test_open_close():
     try:
-        for s in tempClientConnection():
+        for _ in tempClientConnection():
             pass
-    except:
+    except Exception:
         assert False
 
 def test_send_contact_info1(ClientConnection, MsgContactInfo, MsgContactResp):
@@ -199,14 +199,14 @@ def test_send_ctrl_data(ClientConnection, MsgTimeStampReq, MsgTimeStampResp, Msg
     s = ClientConnection  
     try:
         s.sendall(MsgTimeStampReq)
-        data = s.recv(1024)
+        _ = s.recv(1024)
     except TimeoutError:
         pass
   #  time.sleep(2.5)
   #  assert data == MsgTimeStampResp
     try:
         s.sendall(MsgContollerInd)
-        data = s.recv(1024)
+        _ = s.recv(1024)
     except TimeoutError:
         pass
 
@@ -214,16 +214,16 @@ def test_send_inv_data(ClientConnection, MsgTimeStampReq, MsgTimeStampResp, MsgI
     s = ClientConnection  
     try:
         s.sendall(MsgTimeStampReq)
-        data = s.recv(1024)
+        _ = s.recv(1024)
     except TimeoutError:
         pass
   #  time.sleep(32.5)
   #  assert data == MsgTimeStampResp
     try:
         s.sendall(MsgInvData)
-        data = s.recv(1024)
+        _ = s.recv(1024)
         s.sendall(MsgInverterInd)
-        data = s.recv(1024)
+        _ = s.recv(1024)
     except TimeoutError:
         pass
 
@@ -231,6 +231,6 @@ def test_ota_req(ClientConnection, MsgOtaUpdateReq):
     s = ClientConnection  
     try:
         s.sendall(MsgOtaUpdateReq)
-        data = s.recv(1024)
+        _ = s.recv(1024)
     except TimeoutError:
         pass