Throw better error for when running into k8s service discovery issue (#18209)

Signed-off-by: Will Eaton <weaton@redhat.com>

tests/test_vllm_port.py

@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: Apache-2.0
+
+import os
+from unittest.mock import patch
+
+import pytest
+
+from vllm.envs import get_vllm_port
+
+
+def test_get_vllm_port_not_set():
+    """Test when VLLM_PORT is not set."""
+    with patch.dict(os.environ, {}, clear=True):
+        assert get_vllm_port() is None
+
+
+def test_get_vllm_port_valid():
+    """Test when VLLM_PORT is set to a valid integer."""
+    with patch.dict(os.environ, {"VLLM_PORT": "5678"}, clear=True):
+        assert get_vllm_port() == 5678
+
+
+def test_get_vllm_port_invalid():
+    """Test when VLLM_PORT is set to a non-integer value."""
+    with (patch.dict(os.environ, {"VLLM_PORT": "abc"}, clear=True),
+          pytest.raises(ValueError, match="must be a valid integer")):
+        get_vllm_port()
+
+
+def test_get_vllm_port_uri():
+    """Test when VLLM_PORT is set to a URI."""
+    with (patch.dict(os.environ, {"VLLM_PORT": "tcp://localhost:5678"},
+                     clear=True),
+          pytest.raises(ValueError, match="appears to be a URI")):
+        get_vllm_port()