Update testing docs for new Client API

Author: felixweinberger

docs/testing.md

@@ -1,10 +1,11 @@
 # Testing MCP Servers
 
-If you call yourself a developer, you will want to test your MCP server.
-The Python SDK offers the `create_connected_server_and_client_session` function to create a session
-using an in-memory transport. I know, I know, the name is too long... We are working on improving it.
+The Python SDK provides a `Client` class for testing MCP servers with an in-memory transport.
+This makes it easy to write tests without network overhead.
 
-Anyway, let's assume you have a simple server with a single tool:
+## Basic Usage
+
+Let's assume you have a simple server with a single tool:
 
 ```python title="server.py"
 from mcp.server import FastMCP
@@ -40,12 +41,9 @@ To run the below test, you'll need to install the following dependencies:
     server - you don't need to use it, but we are spreading the word for best practices.
 
 ```python title="test_server.py"
-from collections.abc import AsyncGenerator
-
 import pytest
 from inline_snapshot import snapshot
-from mcp.client.session import ClientSession
-from mcp.shared.memory import create_connected_server_and_client_session
+from mcp import Client
 from mcp.types import CallToolResult, TextContent
 
 from server import app
@@ -56,23 +54,41 @@ def anyio_backend():  # (1)!
     return "asyncio"
 
 
-@pytest.fixture
-async def client_session() -> AsyncGenerator[ClientSession]:
-    async with create_connected_server_and_client_session(app, raise_exceptions=True) as _session:
-        yield _session
-
-
 @pytest.mark.anyio
-async def test_call_add_tool(client_session: ClientSession):
-    result = await client_session.call_tool("add", {"a": 1, "b": 2})
-    assert result == snapshot(
-        CallToolResult(
-            content=[TextContent(type="text", text="3")],
-            structuredContent={"result": 3},
+async def test_call_add_tool():
+    async with Client(app, raise_exceptions=True) as client:
+        result = await client.call_tool("add", {"a": 1, "b": 2})
+        assert result == snapshot(
+            CallToolResult(
+                content=[TextContent(type="text", text="3")],
+                structuredContent={"result": 3},
+            )
         )
-    )
 ```
 
 1. If you are using `trio`, you should set `"trio"` as the `anyio_backend`. Check more information in the [anyio documentation](https://anyio.readthedocs.io/en/stable/testing.html#specifying-the-backends-to-run-on).
 
 There you go! You can now extend your tests to cover more scenarios.
+
+## Advanced: Low-Level Transport Access
+
+For tests that need direct access to the underlying `ClientSession`, use `InMemoryTransport`:
+
+```python
+from mcp.client.session import ClientSession
+from mcp.client.transports import InMemoryTransport
+
+from server import app
+
+
+async def test_with_low_level_access():
+    transport = InMemoryTransport(app, raise_exceptions=True)
+    async with transport.connect() as (read_stream, write_stream):
+        async with ClientSession(read_stream, write_stream) as session:
+            await session.initialize()
+            # Direct access to the full ClientSession API
+            result = await session.call_tool("add", {"a": 1, "b": 2})
+```
+
+The `Client` class is built on top of `InMemoryTransport` and handles initialization automatically.
+Use `InMemoryTransport` directly only when you need fine-grained control over the session lifecycle.

src/mcp/client/client.py

@@ -92,9 +92,7 @@ async def __aenter__(self) -> Client:
         try:
             # Create transport and connect
             transport = InMemoryTransport(self._server, raise_exceptions=self._raise_exceptions)
-            read_stream, write_stream = await self._exit_stack.enter_async_context(
-                transport.connect()
-            )
+            read_stream, write_stream = await self._exit_stack.enter_async_context(transport.connect())
 
             # Create session
             self._session = await self._exit_stack.enter_async_context(

src/mcp/client/transports/memory.py

@@ -33,7 +33,7 @@ class InMemoryTransport:
                 # Use the session...
 
     Or more commonly, use with Client:
-        async with Client.from_server(server) as client:
+        async with Client(server) as client:
             result = await client.call_tool("my_tool", {...})
     """
 

tests/issues/test_141_resource_templates.py

@@ -77,7 +77,6 @@ def get_user_profile(user_id: str) -> str:
         return f"Profile for user {user_id}"
 
     async with Client(mcp) as session:
-
         # List available resources
         resources = await session.list_resource_templates()
         assert isinstance(resources, ListResourceTemplatesResult)