Method on_container_start

cpp/src/context_test.cpp:75–82

    test_server (const std::string &s) : url(s) {}

    void on_container_start(proton::container &c) override {
        listener = c.listen(url, listen_handler);

        std::string data = "listener-user-data";
        // Set user context 'data' on listener.
        listener.user_data(&data);
        ASSERT_EQUAL(&data, listener.user_data());
    }

    void on_message(proton::delivery &d, proton::message &msg) override {
        std::string data = "delivery-user-data";