test(client): cover resume path and streamable-http get-stream guard

Author: mrutunjay-kinagi

tests/client/test_session.py

@@ -606,6 +606,28 @@ async def mock_server():
         assert result.protocol_version == LATEST_PROTOCOL_VERSION
 
 
+@pytest.mark.anyio
+async def test_client_session_resume_sets_initialize_result():
+    client_to_server_send, client_to_server_receive = anyio.create_memory_object_stream[SessionMessage](1)
+    server_to_client_send, server_to_client_receive = anyio.create_memory_object_stream[SessionMessage](1)
+
+    session = ClientSession(server_to_client_receive, client_to_server_send)
+    assert session.initialize_result is None
+
+    resumed_result = InitializeResult(
+        protocol_version=LATEST_PROTOCOL_VERSION,
+        capabilities=ServerCapabilities(),
+        server_info=Implementation(name="mock-server", version="0.1.0"),
+    )
+    session.resume(resumed_result)
+    assert session.initialize_result == resumed_result
+
+    await client_to_server_send.aclose()
+    await client_to_server_receive.aclose()
+    await server_to_client_send.aclose()
+    await server_to_client_receive.aclose()
+
+
 @pytest.mark.anyio
 @pytest.mark.parametrize(argnames="meta", argvalues=[None, {"toolMeta": "value"}])
 async def test_client_tool_call_with_meta(meta: RequestParamsMeta | None):

tests/shared/test_streamable_http.py

@@ -1809,6 +1809,46 @@ def test_streamable_http_transport_includes_seeded_session_id_header():
     assert headers["mcp-session-id"] == "resume-session-id"
 
 
+@pytest.mark.anyio
+async def test_streamable_http_client_resumption_starts_get_stream_once(monkeypatch: pytest.MonkeyPatch):
+    start_count = 0
+
+    async def fake_handle_get_stream(
+        self: StreamableHTTPTransport,
+        client: httpx.AsyncClient,
+        read_stream_writer: anyio.abc.ObjectSendStream[SessionMessage | Exception],
+    ) -> None:
+        nonlocal start_count
+        start_count += 1
+        await anyio.sleep(0)
+
+    async def fake_post_writer(
+        self: StreamableHTTPTransport,
+        client: httpx.AsyncClient,
+        write_stream_reader: anyio.abc.ObjectReceiveStream[SessionMessage],
+        read_stream_writer: anyio.abc.ObjectSendStream[SessionMessage | Exception],
+        write_stream: anyio.abc.ObjectSendStream[SessionMessage],
+        start_get_stream: Any,
+        tg: anyio.abc.TaskGroup,
+    ) -> None:
+        # Call twice; the second call should hit the early return guard.
+        start_get_stream()
+        start_get_stream()
+        await anyio.sleep(0)
+
+    monkeypatch.setattr(StreamableHTTPTransport, "handle_get_stream", fake_handle_get_stream)
+    monkeypatch.setattr(StreamableHTTPTransport, "post_writer", fake_post_writer)
+
+    async with streamable_http_client(
+        "http://localhost:8000/mcp",
+        session_id="resume-session-id",
+        terminate_on_close=False,
+    ):
+        await anyio.sleep(0)
+
+    assert start_count == 1
+
+
 @pytest.mark.anyio
 async def test_priming_event_not_sent_for_old_protocol_version():
     """Test that _maybe_send_priming_event skips for old protocol versions (backwards compat)."""