saved_handler is a public interface:

This container allows completion handlers to be safely
suspended and resumed later, or destroyed.

test/beast/core/saved_handler.cpp

@@ -0,0 +1,158 @@
+//
+// Copyright (c) 2016-2017 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)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+// Test that header file is self-contained.
+#include <boost/beast/core/saved_handler.hpp>
+
+#include <boost/beast/_experimental/unit_test/suite.hpp>
+#include <stdexcept>
+
+namespace boost {
+namespace beast {
+
+//------------------------------------------------------------------------------
+
+class saved_handler_test : public unit_test::suite
+{
+public:
+    class handler
+    {
+        unit_test::suite& s_;
+        bool failed_ = true;
+        bool throw_on_move_ = false;
+    
+    public:
+        handler(handler const&) = delete;
+        handler& operator=(handler&&) = delete;
+        handler& operator=(handler const&) = delete;
+
+        ~handler()
+        {
+            s_.BEAST_EXPECT(! failed_);
+        }
+
+        explicit
+        handler(unit_test::suite& s)
+            : s_(s)
+        {
+        }
+
+        handler(handler&& other)
+            : s_(other.s_)
+            , failed_(boost::exchange(
+                other.failed_, false))
+        {
+            if(throw_on_move_)
+                throw std::bad_alloc{};
+        }
+
+        void
+        operator()()
+        {
+            failed_ = false;
+        }
+    };
+
+    class unhandler
+    {
+        unit_test::suite& s_;
+        bool invoked_ = false;
+   
+    public:
+        unhandler(unhandler const&) = delete;
+        unhandler& operator=(unhandler&&) = delete;
+        unhandler& operator=(unhandler const&) = delete;
+
+        ~unhandler()
+        {
+            s_.BEAST_EXPECT(! invoked_);
+        }
+
+        explicit
+        unhandler(unit_test::suite& s)
+            : s_(s)
+        {
+        }
+
+        unhandler(unhandler&& other)
+            : s_(other.s_)
+            , invoked_(boost::exchange(
+                other.invoked_, false))
+        {
+        }
+
+        void
+        operator()()
+        {
+            invoked_ = true;
+        }
+    };
+
+    struct throwing_handler
+    {
+        throwing_handler() = default;
+
+        throwing_handler(throwing_handler&&)
+        {
+            BOOST_THROW_EXCEPTION(std::exception{});
+        }
+
+        void
+        operator()()
+        {
+        }
+    };
+
+    void
+    testSavedHandler()
+    {
+        {
+            saved_handler sh;
+            BEAST_EXPECT(! sh.has_value());
+
+            sh.emplace(handler{*this});
+            BEAST_EXPECT(sh.has_value());
+            sh.invoke();
+            BEAST_EXPECT(! sh.has_value());
+
+            sh.emplace(handler{*this}, std::allocator<char>{});
+            BEAST_EXPECT(sh.has_value());
+            sh.invoke();
+            BEAST_EXPECT(! sh.has_value());
+
+            sh.emplace(unhandler{*this});
+            BEAST_EXPECT(sh.has_value());
+        }
+
+        {
+            saved_handler sh;
+            try
+            {
+                sh.emplace(throwing_handler{});
+                fail();
+            }
+            catch(std::exception const&)
+            {
+                pass();
+            }
+            BEAST_EXPECT(! sh.has_value());
+        }
+    }
+
+    void
+    run() override
+    {
+        testSavedHandler();
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(beast,core,saved_handler);
+
+} // beast
+} // boost