fix: detect cross-node multimodal transport by nnodes (#35646)

test/registered/unit/multimodal/test_tensor_transport_mode.py

@@ -0,0 +1,37 @@
+"""Tests for multimodal tensor transport topology detection."""
+
+import unittest
+from types import SimpleNamespace
+from unittest.mock import patch
+
+from sglang.srt.multimodal.transport import determine_tensor_transport_mode
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=1, suite="base-a-test-cpu")
+
+
+class TestTensorTransportMode(CustomTestCase):
+    def test_transport_mode_uses_published_node_topology(self):
+        cases = (
+            (1, None, "cuda_ipc"),
+            (1, "127.0.0.1:20000", "cuda_ipc"),
+            (2, None, "default"),
+            (2, "10.0.0.1:20000", "default"),
+        )
+
+        for nnodes, dist_init_addr, expected in cases:
+            with self.subTest(nnodes=nnodes, dist_init_addr=dist_init_addr):
+                parallel = SimpleNamespace(
+                    nnodes=nnodes,
+                    dist_init_addr=dist_init_addr,
+                )
+                with patch(
+                    "sglang.srt.multimodal.transport.get_parallel",
+                    return_value=parallel,
+                ):
+                    self.assertEqual(determine_tensor_transport_mode(), expected)
+
+
+if __name__ == "__main__":
+    unittest.main()