fixed multicast updated tests

Test/Configurations/TestApp.cfg

@@ -424,6 +424,7 @@ $TestApp = {
             Port = 44500
             MulticastGroup = "239.0.0.1"
             DataPort = 44503
+            Interface = "127.0.0.1"
             MaxPayloadSize = 1400
             PublishingMode = "Accumulate"
             MinRefreshRate = 100

Test/Configurations/combined_test.cfg

@@ -279,6 +279,7 @@ $App = {
             Port = 44500
             MulticastGroup = "239.0.0.1"
             DataPort = 44503
+            Interface = "127.0.0.1"
             MaxPayloadSize = 1400
             PublishingMode = "Accumulate"
             MinRefreshRate = 100

Test/Configurations/streamhub_demo.cfg

@@ -411,6 +411,7 @@ $App = {
       Port = 44500
       MulticastGroup = "239.0.0.1"
       DataPort = 44503
+      Interface = "127.0.0.1"
       MaxPayloadSize = 1400
       PublishingMode = "Accumulate"
       MinRefreshRate = 100

Test/E2E/datasources/E2EMulticastTest.cfg

@@ -64,6 +64,7 @@ $E2EMulticastTest = {
             Port = 44600
             MulticastGroup = "239.0.0.1"
             DataPort = 44610
+            Interface = "127.0.0.1"
             MaxPayloadSize = 65507
             PublishingMode = "Strict"
             Signals = {

Test/E2E/suite/gen_cfg.py

@@ -17,6 +17,8 @@ expected, not an error.
 """
 import argparse
 import os
+import re
+import subprocess
 import sys
 
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
@@ -25,6 +27,41 @@ import scenarios as S  # noqa: E402
 PRODUCER_HZ = 1000      # LinuxTimer frequency (Hz)
 
 
+def _iface_to_ip(name):
+    """Resolve a network interface name (e.g. ``"wlan0"``) to its first IPv4
+    address via ``ip -4 addr show <name>``.  Returns ``"127.0.0.1"`` on failure."""
+    try:
+        out = subprocess.check_output(
+            ["ip", "-4", "addr", "show", name],
+            stderr=subprocess.DEVNULL, text=True)
+        m = re.search(r"inet\s+(\d+\.\d+\.\d+\.\d+)", out)
+        if m:
+            return m.group(1)
+    except (subprocess.CalledProcessError, FileNotFoundError, OSError):
+        pass
+    return "127.0.0.1"
+
+
+def _mcast_interface_ip(group):
+    """Return the IPv4 address of the OS-selected interface for a multicast
+    group.  MARTe2's ``BasicUDPSocket::Join`` expects an IP address (passed to
+    ``inet_addr``), not an interface name.
+
+    Uses ``ip route get <group>`` to find the outgoing device, then resolves
+    its IP.  Falls back to ``"127.0.0.1"`` if the route or device lookup fails.
+    """
+    try:
+        out = subprocess.check_output(
+            ["ip", "route", "get", group],
+            stderr=subprocess.DEVNULL, text=True)
+        m = re.search(r"dev\s+(\S+)", out)
+        if m:
+            return _iface_to_ip(m.group(1))
+    except (subprocess.CalledProcessError, FileNotFoundError, OSError):
+        pass
+    return "127.0.0.1"
+
+
 def _ndims(elements):
     return 0 if elements == 1 else 1
 
@@ -78,6 +115,8 @@ def _streamer_block(src, scenario):
     if scenario["network"] == "multicast":
         parts.append(f'MulticastGroup = "{src["multicast_group"]}"')
         parts.append(f"DataPort = {src['data_port']}")
+        iface = src.get("interface") or _mcast_interface_ip(src["multicast_group"])
+        parts.append(f'Interface = "{iface}"')
     sigs = " ".join(_streamer_sig(sig) for sig in s)
     return (f"        +Streamer_{src['id']} = {{ Class = UDPStreamer "
             f"{' '.join(parts)} Signals = {{ {sigs} }} }}")