Add end-to-end tests for server-client communication

This commit introduces end-to-end tests to detect potential miscommunication issues between servers and clients (e.g. modelcontextprotocol#280).

The implementation includes:
- Basic end-to-end test suite using an Echo server
- Verification of session initialization
- Testing of resource templates, tools, and prompts listing functionality

Author: jkawamoto

tests/test_e2e.py

@@ -0,0 +1,65 @@
+from typing import AsyncGenerator
+
+import pytest
+
+from mcp import StdioServerParameters, ClientSession, stdio_client
+from mcp.server import FastMCP
+
+params = StdioServerParameters(command="uv", args=["run", __file__])
+
+
+def server() -> FastMCP:
+    mcp = FastMCP("Echo")
+
+    @mcp.resource("echo://{message}")
+    def echo_resource(message: str) -> str:
+        """Echo a message as a resource"""
+        return f"Resource echo: {message}"
+
+    @mcp.tool()
+    def echo_tool(message: str) -> str:
+        """Echo a message as a tool"""
+        return f"Tool echo: {message}"
+
+    @mcp.prompt()
+    def echo_prompt(message: str) -> str:
+        """Create an echo prompt"""
+        return f"Please process this message: {message}"
+
+    return mcp
+
+
+@pytest.fixture
+async def mcp_client_session() -> AsyncGenerator[ClientSession, None]:
+    async with stdio_client(params) as streams:
+        async with ClientSession(streams[0], streams[1]) as session:
+            await session.initialize()
+            yield session
+
+
+@pytest.mark.anyio
+async def test_list_resource_templates(mcp_client_session: ClientSession) -> None:
+    res = await mcp_client_session.list_resource_templates()
+    templates = set(template.name for template in res.resourceTemplates)
+
+    assert "echo_resource" in templates
+
+
+@pytest.mark.anyio
+async def test_list_tools(mcp_client_session: ClientSession) -> None:
+    res = await mcp_client_session.list_tools()
+    tools = set(tool.name for tool in res.tools)
+
+    assert "echo_tool" in tools
+
+
+@pytest.mark.anyio
+async def test_list_prompts(mcp_client_session: ClientSession) -> None:
+    res = await mcp_client_session.list_prompts()
+    prompts = set(prompt.name for prompt in res.prompts)
+
+    assert "echo_prompt" in prompts
+
+
+if __name__ == "__main__":
+    server().run()