added the testcase for StreamFailure

tests/core/host/test_basic_host.py

@@ -1,3 +1,10 @@
+from unittest.mock import (
+    AsyncMock,
+    MagicMock,
+)
+
+import pytest
+
 from libp2p import (
     new_swarm,
 )
@@ -10,6 +17,9 @@ from libp2p.host.basic_host import (
 from libp2p.host.defaults import (
     get_default_protocols,
 )
+from libp2p.host.exceptions import (
+    StreamFailure,
+)
 
 
 def test_default_protocols():
@@ -22,3 +32,30 @@ def test_default_protocols():
     # NOTE: comparing keys for equality as handlers may be closures that do not compare
     # in the way this test is concerned with
     assert handlers.keys() == get_default_protocols(host).keys()
+
+
+@pytest.mark.trio
+async def test_swarm_stream_handler_no_protocol_selected(monkeypatch):
+    key_pair = create_new_key_pair()
+    swarm = new_swarm(key_pair)
+    host = BasicHost(swarm)
+
+    # Create a mock net_stream
+    net_stream = MagicMock()
+    net_stream.reset = AsyncMock()
+    net_stream.muxed_conn.peer_id = "peer-test"
+
+    # Monkeypatch negotiate to simulate "no protocol selected"
+    async def fake_negotiate(comm, timeout):
+        return None, None
+
+    monkeypatch.setattr(host.multiselect, "negotiate", fake_negotiate)
+
+    # Now run the handler and expect StreamFailure
+    with pytest.raises(
+        StreamFailure, match="Failed to negotiate protocol: no protocol selected"
+    ):
+        await host._swarm_stream_handler(net_stream)
+
+    # Ensure reset was called since negotiation failed
+    net_stream.reset.assert_awaited()