Problem: no tests for poller_t

Solution: add tests

tests/testutil.hpp

@@ -0,0 +1,49 @@
+#pragma once
+
+#include <gtest/gtest.h>
+#include <zmq.hpp>
+
+#if defined(ZMQ_CPP11)
+#include <array>
+
+class loopback_ip4_binder
+{
+public:
+    loopback_ip4_binder(zmq::socket_t &socket) { bind(socket); }
+    std::string endpoint() { return endpoint_; }
+private:
+    // Helper function used in constructor
+    // as Gtest allows ASSERT_* only in void returning functions
+    // and constructor/destructor are not.
+    void bind(zmq::socket_t &socket)
+    {
+        ASSERT_NO_THROW(socket.bind("tcp://127.0.0.1:*"));
+        std::array<char, 100> endpoint{};
+        size_t endpoint_size = endpoint.size();
+        ASSERT_NO_THROW(socket.getsockopt(ZMQ_LAST_ENDPOINT, endpoint.data(),
+                                          &endpoint_size));
+        ASSERT_TRUE(endpoint_size < endpoint.size());
+        endpoint_ = std::string{endpoint.data()};
+    }
+    std::string endpoint_;
+};
+
+struct common_server_client_setup
+{
+    common_server_client_setup ()
+    {
+        init ();
+    }
+
+    void init()
+    {
+        endpoint = loopback_ip4_binder {server}.endpoint ();
+        ASSERT_NO_THROW (client.connect (endpoint));
+    }
+
+    zmq::context_t context;
+    zmq::socket_t server {context, zmq::socket_type::server};
+    zmq::socket_t client {context, zmq::socket_type::client};
+    std::string endpoint;
+};
+#endif