diff --git a/tests/test_main.py b/tests/test_main.py
new file mode 100644
index 0000000..2748653
--- /dev/null
+++ b/tests/test_main.py
@@ -0,0 +1,133 @@
+import sys
+
+import pytest
+
+from modpoll import main
+
+
+def test_mqtt_tls_cli_options_forwarded(monkeypatch):
+    captured = {}
+
+    class FakeMqttHandler:
+        def __init__(
+            self,
+            name,
+            host,
+            port,
+            user,
+            password,
+            clientid,
+            qos,
+            subscribe_topics,
+            use_tls,
+            tls_version,
+            cacerts,
+            insecure,
+            mqtt_version,
+            log_level,
+        ):
+            captured["init"] = {
+                "name": name,
+                "host": host,
+                "port": port,
+                "user": user,
+                "password": password,
+                "clientid": clientid,
+                "qos": qos,
+                "subscribe_topics": subscribe_topics,
+                "use_tls": use_tls,
+                "tls_version": tls_version,
+                "cacerts": cacerts,
+                "insecure": insecure,
+                "mqtt_version": mqtt_version,
+                "log_level": log_level,
+            }
+
+        def setup(self):
+            return True
+
+        def connect(self):
+            return True
+
+        def close(self):
+            captured["closed"] = True
+
+        def receive(self):
+            return None, None
+
+    def fake_setup_modbus_handlers(args, mqtt_handler):
+        captured["handler_instance"] = mqtt_handler
+        # Stop execution before entering the main polling loop
+        raise SystemExit(0)
+
+    monkeypatch.setattr(main, "MqttHandler", FakeMqttHandler)
+    monkeypatch.setattr(main, "setup_modbus_handlers", fake_setup_modbus_handlers)
+    monkeypatch.setattr(
+        sys,
+        "argv",
+        [
+            "modpoll",
+            "--config",
+            "dummy.csv",
+            "--tcp",
+            "127.0.0.1",
+            "--mqtt-host",
+            "broker.local",
+            "--mqtt-use-tls",
+            "--mqtt-cacerts",
+            "/tmp/ca.pem",
+            "--mqtt-tls-version",
+            "tlsv1.2",
+            "--mqtt-version",
+            "3.1.1",
+            "--mqtt-insecure",
+        ],
+    )
+
+    with pytest.raises(SystemExit) as excinfo:
+        main.app()
+
+    assert excinfo.value.code == 0
+    init_args = captured["init"]
+    assert init_args["use_tls"] is True
+    assert init_args["tls_version"] == "tlsv1.2"
+    assert init_args["cacerts"] == "/tmp/ca.pem"
+    assert init_args["insecure"] is True
+    assert init_args["mqtt_version"] == "3.1.1"
+    assert init_args["subscribe_topics"] == ["modpoll/+/set"]
+
+
+def test_mqtt_setup_close_errors_are_suppressed(monkeypatch):
+    class FakeMqttHandler:
+        def __init__(self, *args, **kwargs):
+            pass
+
+        def setup(self):
+            raise RuntimeError("setup failed")
+
+        def connect(self):
+            return False
+
+        def close(self):
+            raise RuntimeError("close exploded")
+
+    monkeypatch.setattr(main, "MqttHandler", FakeMqttHandler)
+    monkeypatch.setattr(main, "setup_modbus_handlers", lambda args, mqtt_handler: [])
+    monkeypatch.setattr(
+        sys,
+        "argv",
+        [
+            "modpoll",
+            "--config",
+            "dummy.csv",
+            "--tcp",
+            "127.0.0.1",
+            "--mqtt-host",
+            "broker.local",
+        ],
+    )
+
+    with pytest.raises(SystemExit) as excinfo:
+        main.app()
+
+    assert excinfo.value.code == 1
diff --git a/tests/test_modbus_task.py b/tests/test_modbus_task.py
index 5907ae7..d9074d3 100644
--- a/tests/test_modbus_task.py
+++ b/tests/test_modbus_task.py
@@ -1,8 +1,9 @@
-import pytest
+import pytest  # type: ignore
 from modpoll.arg_parser import get_parser
 from modpoll.modbus_task import setup_modbus_handlers
 
 
+@pytest.mark.integration
 def test_modbus_task_modbus_setup():
     parser = get_parser()
     args = parser.parse_args(
diff --git a/tests/test_mqtt_task.py b/tests/test_mqtt_task.py
index a184fb9..8ca084d 100644
--- a/tests/test_mqtt_task.py
+++ b/tests/test_mqtt_task.py
@@ -26,6 +26,160 @@ def test_mqtt_task_setup():
     mqtt_handler.close()
 
 
+def test_receive_empty_queue_returns_none():
+    handler = MqttHandler(
+        name="test_mqtt",
+        host="broker.emqx.io",
+        port=1883,
+        user=None,
+        password=None,
+        clientid="test_client_13579",
+        qos=0,
+    )
+
+    topic, payload = handler.receive()
+
+    assert topic is None
+    assert payload is None
+
+
+def test_receive_returns_message_when_available():
+    handler = MqttHandler(
+        name="test_mqtt",
+        host="broker.emqx.io",
+        port=1883,
+        user=None,
+        password=None,
+        clientid="test_client_13579",
+        qos=0,
+    )
+
+    class FakeQueue:
+        def get(self, block=False):
+            return ("some/topic", b"payload")
+
+    handler.rx_queue = FakeQueue()
+
+    topic, payload = handler.receive()
+
+    assert topic == "some/topic"
+    assert payload == b"payload"
+
+
+def test_publish_when_connected_calls_client_publish():
+    handler = MqttHandler(
+        name="test_mqtt",
+        host="broker.emqx.io",
+        port=1883,
+        user=None,
+        password=None,
+        clientid="test_client_13579",
+        qos=1,
+    )
+
+    class StubClient:
+        def __init__(self):
+            self.calls = []
+
+        def is_connected(self):
+            return True
+
+        def publish(self, topic, msg, qos, retain):
+            self.calls.append((topic, msg, qos, retain))
+
+            class PubInfo:
+                rc = 0
+
+            return PubInfo()
+
+    stub = StubClient()
+    handler.mqtt_client = stub
+
+    result = handler.publish("topic", "message", qos=2, retain=True)
+
+    assert result.rc == 0
+    assert stub.calls == [("topic", "message", 2, True)]
+
+
+def test_setup_respects_tls_option(monkeypatch):
+    called = {}
+    handler = MqttHandler(
+        name="test_mqtt",
+        host="broker.emqx.io",
+        port=8883,
+        user=None,
+        password=None,
+        clientid="client",
+        qos=0,
+        subscribe_topics=["secure/topic"],
+        use_tls=True,
+        tls_version="tlsv1.2",
+        mqtt_version="3.1.1",
+    )
+
+    def fake_setup_tls():
+        called["tls"] = True
+
+    monkeypatch.setattr(handler, "_setup_tls", fake_setup_tls)
+
+    assert handler.setup()
+    assert called.get("tls") is True
+    assert handler.mqtt_client is not None
+
+
+def test_publish_skips_when_disconnected_qos0(monkeypatch):
+    handler = MqttHandler(
+        name="test_mqtt",
+        host="broker.emqx.io",
+        port=1883,
+        user=None,
+        password=None,
+        clientid="test_client_13579",
+        qos=0,
+    )
+
+    class StubClient:
+        def is_connected(self):
+            return False
+
+    handler.mqtt_client = StubClient()
+
+    result = handler.publish("topic", "msg")
+
+    assert result is None
+
+
+def test_publish_attempts_reconnect_when_disconnected_qos1(monkeypatch):
+    handler = MqttHandler(
+        name="test_mqtt",
+        host="broker.emqx.io",
+        port=1883,
+        user=None,
+        password=None,
+        clientid="test_client_13579",
+        qos=1,
+    )
+
+    class StubClient:
+        def is_connected(self):
+            return False
+
+    handler.mqtt_client = StubClient()
+
+    called = {}
+
+    def fake_connect():
+        called["connect"] = True
+        return False
+
+    monkeypatch.setattr(handler, "connect", fake_connect)
+
+    result = handler.publish("topic", "msg")
+
+    assert result is None
+    assert called.get("connect") is True
+
+
 @pytest.mark.integration
 def test_mqtt_task_connect():
     mqtt_handler = MqttHandler(