test: interaction-model end-to-end suite with a requirements manifest (#2691)

tests/interaction/lowlevel/test_ping.py

@@ -0,0 +1,53 @@
+"""Ping interactions against the low-level Server, driven through the public Client API."""
+
+import pytest
+from inline_snapshot import snapshot
+
+from mcp import types
+from mcp.server import Server, ServerRequestContext
+from mcp.types import CallToolResult, EmptyResult, TextContent
+from tests.interaction._connect import Connect
+from tests.interaction._requirements import requirement
+
+pytestmark = pytest.mark.anyio
+
+
+@requirement("lifecycle:ping")
+@requirement("ping:client-to-server")
+async def test_client_ping_returns_empty_result(connect: Connect) -> None:
+    """A client ping is answered with an empty result, even by a server with no handlers."""
+    server = Server("silent")
+
+    async with connect(server) as client:
+        result = await client.send_ping()
+
+    assert result == snapshot(EmptyResult())
+
+
+@requirement("lifecycle:ping")
+@requirement("ping:server-to-client")
+async def test_server_ping_returns_empty_result(connect: Connect) -> None:
+    """A server-initiated ping sent while a request is in flight is answered by the client.
+
+    The tool returns the type of the ping response, proving the round trip completed inside
+    the handler before the tool result was produced.
+    """
+
+    async def list_tools(
+        ctx: ServerRequestContext, params: types.PaginatedRequestParams | None
+    ) -> types.ListToolsResult:
+        return types.ListToolsResult(
+            tools=[types.Tool(name="ping_back", description="Ping the client.", input_schema={"type": "object"})]
+        )
+
+    async def call_tool(ctx: ServerRequestContext, params: types.CallToolRequestParams) -> CallToolResult:
+        assert params.name == "ping_back"
+        pong = await ctx.session.send_ping()
+        return CallToolResult(content=[TextContent(text=type(pong).__name__)])
+
+    server = Server("pinger", on_list_tools=list_tools, on_call_tool=call_tool)
+
+    async with connect(server) as client:
+        result = await client.call_tool("ping_back", {})
+
+    assert result == snapshot(CallToolResult(content=[TextContent(text="EmptyResult")]))