Test case for UDP issue

test/conftest.py

@@ -1,6 +1,7 @@
 """Configure pytest."""
 import functools
 import platform
+from collections import deque
 
 import pytest
 
@@ -132,6 +133,64 @@ def setblocking(self, _flag):
         """Set blocking."""
         return None
 
+class mockSocket2:  # pylint: disable=invalid-name
+    """Mock socket."""
+
+    timeout = 2
+
+    def __init__(self):
+        """Initialize."""
+        self.receive = deque()
+        self.send = deque()
+
+    def mock_prepare_receive(self, msg):
+        """Store message."""
+        self.receive.append(msg);
+
+    def mock_read_sent(self):
+        self.send.popleft()
+
+    def mock_retrieve(self, size):
+        """Get message."""
+        if len(self.receive) == 0 or not size: 
+            return b"";
+        if size >= len(self.receive[0]):
+            retval = self.receive.popleft()
+        else:
+            retval = self.receive[0][0:size]
+            self.data[0] = self.receive[0][size:-1]
+        return retval
+
+    def close(self):
+        """Close."""
+        return True
+
+    def recv(self, size):
+        """Receive."""
+        return self.mock_retrieve(size)
+
+    def read(self, size):
+        """Read."""
+        return self.mock_retrieve(size)
+
+    def send(self, msg):
+        """Send."""
+        self.mock_store(msg)
+        return len(msg)
+
+    def recvfrom(self, size):
+        """Receive from."""
+        return [self.mock_retrieve(size)]
+
+    def sendto(self, msg, *_args):
+        """Send to."""
+        self.send.append(msg)
+        return len(msg)
+
+    def setblocking(self, _flag):
+        """Set blocking."""
+        return None
+
 
 def run_coroutine(coro):
     """Run a coroutine as top-level task by iterating through all yielded steps."""

test/test_client_sync.py

@@ -2,6 +2,7 @@
 import ssl
 from itertools import count
 from test.conftest import mockSocket
+from test.conftest import mockSocket2
 from unittest import mock
 
 import pytest
@@ -79,6 +80,27 @@ def test_udp_client_recv(self):
         assert client.recv(0) == b""
         assert client.recv(4) == b"\x00" * 4
 
+    def test_udp_client_recv_duplicate(self):
+        """Test the udp client receive method"""
+        client = ModbusUdpClient("127.0.0.1")
+
+        client.socket = mockSocket2()
+        client.socket.mock_prepare_receive(b"\x00\x01\x00\x00\x00\x05\x01\x04\x02\x00\x03");            # Response 1
+        reply1 = client.read_input_registers(0x820, 1, 1)
+        client.socket.mock_prepare_receive(b"\x00\x01\x00\x00\x00\x05\x01\x04\x02\x00\x03");            # Duplicate response 1
+        client.socket.mock_prepare_receive(b"\x00\x02\x00\x00\x00\x07\x01\x04\x04\x00\x03\xf6\x3e")     # Response 2
+        reply2 = client.read_input_registers(0x820, 2, 1)
+        reply3 = client.read_input_registers(0x820, 100, 1)
+
+        print(reply1.registers)
+        print(reply2.registers)
+        print(reply3.registers)
+        print(reply1.transaction_id)
+        print(reply2.transaction_id)
+        print(reply3.transaction_id)
+
+        assert 1 == 0
+
     def test_udp_client_repr(self):
         """Test udp client representation."""
         client = ModbusUdpClient("127.0.0.1")