Beast.WebSocket:

Beast.WebSocket provides developers with a robust WebSocket
implementation built on Boost.Asio with a consistent asynchronous
model using a modern C++ approach.

src/beast/test/basic_streambuf.cpp

@@ -0,0 +1,9 @@
+//
+// Copyright (c) 2013-2016 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+// Test that header file is self-contained.
+#include <beast/asio/basic_streambuf.h>