Add test demonstrating issue #1027 and verifying PR #1044 fixes it

This test shows that MCP server cleanup code in lifespan doesn't run
when the process is terminated, but does run when stdin is closed first
(as implemented in PR #1044).

The test includes:
- Demonstration of current broken behavior (cleanup doesn't run)
- Verification that stdin closure allows graceful shutdown
- Windows-specific ResourceWarning handling
- Detailed documentation of the issue and solution

Github-Issue:#1027

Author: felixweinberger

tests/issues/test_1027_win_unreachable_cleanup.py

@@ -0,0 +1,237 @@
+"""
+Regression test for issue #1027: Ensure cleanup procedures run properly during shutdown
+
+Issue #1027 reported that cleanup code after "yield" in lifespan was unreachable when
+processes were terminated. This has been fixed by implementing the MCP spec-compliant
+stdio shutdown sequence that closes stdin first, allowing graceful exit.
+
+These tests verify the fix continues to work correctly across all platforms.
+"""
+
+import asyncio
+import sys
+import tempfile
+import textwrap
+from pathlib import Path
+
+import anyio
+import pytest
+
+from mcp import ClientSession, StdioServerParameters
+from mcp.client.stdio import _create_platform_compatible_process, stdio_client
+
+
+@pytest.mark.anyio
+async def test_lifespan_cleanup_executed():
+    """
+    Regression test ensuring MCP server cleanup code runs during shutdown.
+
+    This test verifies that the fix for issue #1027 works correctly by:
+    1. Starting an MCP server that writes a marker file on startup
+    2. Shutting down the server normally via stdio_client
+    3. Verifying the cleanup code (after yield) executed and wrote its marker file
+
+    The fix implements proper stdin closure before termination, giving servers
+    time to run their cleanup handlers.
+    """
+
+    # Create marker files to track server lifecycle
+    with tempfile.NamedTemporaryFile(mode="w", delete=False, suffix=".txt") as f:
+        startup_marker = f.name
+    with tempfile.NamedTemporaryFile(mode="w", delete=False, suffix=".txt") as f:
+        cleanup_marker = f.name
+
+    # Remove the files so we can detect when they're created
+    Path(startup_marker).unlink()
+    Path(cleanup_marker).unlink()
+
+    # Create a minimal MCP server using FastMCP that tracks lifecycle
+    server_code = textwrap.dedent(f"""
+        import asyncio
+        import sys
+        from pathlib import Path
+        from contextlib import asynccontextmanager
+        from mcp.server.fastmcp import FastMCP
+        
+        STARTUP_MARKER = {repr(startup_marker)}
+        CLEANUP_MARKER = {repr(cleanup_marker)}
+        
+        @asynccontextmanager
+        async def lifespan(server):
+            # Write startup marker
+            Path(STARTUP_MARKER).write_text("started")
+            try:
+                yield {{"started": True}}
+            finally:
+                # This cleanup code now runs properly during shutdown
+                Path(CLEANUP_MARKER).write_text("cleaned up")
+        
+        mcp = FastMCP("test-server", lifespan=lifespan)
+        
+        @mcp.tool()
+        def echo(text: str) -> str:
+            return text
+        
+        if __name__ == "__main__":
+            mcp.run()
+    """)
+
+    # Write the server script to a temporary file
+    with tempfile.NamedTemporaryFile(mode="w", delete=False, suffix=".py") as f:
+        server_script = f.name
+        f.write(server_code)
+
+    try:
+        # Launch the MCP server
+        params = StdioServerParameters(command=sys.executable, args=[server_script])
+
+        async with stdio_client(params) as (read, write):
+            async with ClientSession(read, write) as session:
+                # Initialize the session
+                result = await session.initialize()
+                assert result.protocolVersion in ["2024-11-05", "2025-06-18"]
+
+                # Verify startup marker was created
+                assert Path(startup_marker).exists(), "Server startup marker not created"
+                assert Path(startup_marker).read_text() == "started"
+
+                # Make a test request to ensure server is working
+                response = await session.call_tool("echo", {"text": "hello"})
+                assert response.content[0].type == "text"
+                assert getattr(response.content[0], "text") == "hello"
+
+                # Session will be closed when exiting the context manager
+
+        # Give server a moment to complete cleanup
+        await asyncio.sleep(0.5)
+
+        # Verify cleanup marker was created - this works now that stdio_client
+        # properly closes stdin before termination, allowing graceful shutdown
+        assert Path(cleanup_marker).exists(), "Server cleanup marker not created - regression in issue #1027 fix"
+        assert Path(cleanup_marker).read_text() == "cleaned up"
+
+    finally:
+        # Clean up files
+        for path in [server_script, startup_marker, cleanup_marker]:
+            try:
+                Path(path).unlink()
+            except FileNotFoundError:
+                pass
+
+
+@pytest.mark.anyio
+@pytest.mark.filterwarnings("ignore::ResourceWarning" if sys.platform == "win32" else "default")
+async def test_stdin_close_triggers_cleanup():
+    """
+    Regression test verifying the stdin-based graceful shutdown mechanism.
+
+    This test ensures the core fix for issue #1027 continues to work by:
+    1. Manually managing a server process
+    2. Closing stdin to trigger graceful shutdown
+    3. Verifying cleanup handlers run before the process exits
+
+    This mimics the behavior now implemented in stdio_client's shutdown sequence.
+
+    Note on Windows ResourceWarning:
+    On Windows, we may see ResourceWarning about unclosed file descriptors.
+    This is expected behavior because:
+    - We're manually managing the process lifecycle
+    - Windows file handle cleanup works differently than Unix
+    - The warning doesn't indicate a real issue - cleanup still works
+    We filter this warning on Windows only to avoid test noise.
+    """
+
+    # Create marker files to track server lifecycle
+    with tempfile.NamedTemporaryFile(mode="w", delete=False, suffix=".txt") as f:
+        startup_marker = f.name
+    with tempfile.NamedTemporaryFile(mode="w", delete=False, suffix=".txt") as f:
+        cleanup_marker = f.name
+
+    # Remove the files so we can detect when they're created
+    Path(startup_marker).unlink()
+    Path(cleanup_marker).unlink()
+
+    # Create an MCP server that handles stdin closure gracefully
+    server_code = textwrap.dedent(f"""
+        import asyncio
+        import sys
+        from pathlib import Path
+        from contextlib import asynccontextmanager
+        from mcp.server.fastmcp import FastMCP
+        
+        STARTUP_MARKER = {repr(startup_marker)}
+        CLEANUP_MARKER = {repr(cleanup_marker)}
+        
+        @asynccontextmanager
+        async def lifespan(server):
+            # Write startup marker
+            Path(STARTUP_MARKER).write_text("started")
+            try:
+                yield {{"started": True}}
+            finally:
+                # This cleanup code runs when stdin closes, enabling graceful shutdown
+                Path(CLEANUP_MARKER).write_text("cleaned up")
+        
+        mcp = FastMCP("test-server", lifespan=lifespan)
+        
+        @mcp.tool()
+        def echo(text: str) -> str:
+            return text
+        
+        if __name__ == "__main__":
+            # The server should exit gracefully when stdin closes
+            try:
+                mcp.run()
+            except Exception:
+                # Server might get EOF or other errors when stdin closes
+                pass
+    """)
+
+    # Write the server script to a temporary file
+    with tempfile.NamedTemporaryFile(mode="w", delete=False, suffix=".py") as f:
+        server_script = f.name
+        f.write(server_code)
+
+    try:
+        # This test manually manages the process to verify stdin-based shutdown
+        # Start the server process
+        process = await _create_platform_compatible_process(
+            command=sys.executable, args=[server_script], env=None, errlog=sys.stderr, cwd=None
+        )
+
+        # Wait for server to start
+        await asyncio.sleep(1.0)  # Give more time on Windows
+
+        # Check if process is still running
+        if hasattr(process, "returncode") and process.returncode is not None:
+            pytest.fail(f"Server process exited with code {process.returncode}")
+
+        assert Path(startup_marker).exists(), "Server startup marker not created"
+
+        # Close stdin to signal shutdown
+        if process.stdin:
+            await process.stdin.aclose()
+
+        # Wait for process to exit gracefully
+        try:
+            with anyio.fail_after(2.0):
+                await process.wait()
+        except TimeoutError:
+            # If it doesn't exit after stdin close, terminate it
+            process.terminate()
+            await process.wait()
+
+        # Check if cleanup ran
+        await asyncio.sleep(0.5)
+
+        # Verify the cleanup ran - stdin closure enables graceful shutdown
+        assert Path(cleanup_marker).exists(), "Server cleanup marker not created - stdin-based shutdown failed"
+        assert Path(cleanup_marker).read_text() == "cleaned up"
+
+    finally:
+        # Clean up files
+        for path in [server_script, startup_marker, cleanup_marker]:
+            try:
+                Path(path).unlink()
+            except FileNotFoundError:
+                pass