Problem: no tests without ZAP handler where one is expected

Solution: added test case for NULL/PLAIN/CURVE

tests/test_security_zap.cpp

@@ -266,6 +266,20 @@ void test_zap_errors (socket_config_fn server_socket_config_,
                                       client_socket_config_data_);
     shutdown_context_and_server_side (ctx, zap_thread, server, server_mon,
                                       handler);
+    //  no ZAP handler
+    fprintf (stderr, "test_zap_unsuccessful no ZAP handler started\n");
+    setup_context_and_server_side (
+      &ctx, &handler, &zap_thread, &server, &server_mon, my_endpoint,
+      NULL, server_socket_config_);
+    test_zap_unsuccessful (ctx, my_endpoint, server, server_mon,
+#ifdef ZMQ_BUILD_DRAFT_API
+                           ZMQ_EVENT_HANDSHAKE_FAILED_NO_DETAIL, EFAULT,
+#else
+                           0, 0,
+#endif
+                           client_socket_config_, client_socket_config_data_);
+    shutdown_context_and_server_side (ctx, zap_thread, server, server_mon,
+                                      handler);
 }
 
 int main (void)

tests/testutil_security.hpp

@@ -336,12 +336,15 @@ void setup_context_and_server_side (
     int rc = zmq_bind (*handler, "inproc://handler-control");
     assert (rc == 0);
 
-    *zap_thread = zmq_threadstart (zap_handler_, *ctx);
+    if (zap_handler_) {
+        *zap_thread = zmq_threadstart (zap_handler_, *ctx);
 
-    char *buf = s_recv (*handler);
-    assert (buf);
-    assert (streq (buf, "GO"));
-    free (buf);
+        char *buf = s_recv (*handler);
+        assert (buf);
+        assert (streq (buf, "GO"));
+        free (buf);
+    } else
+        *zap_thread = NULL;
 
     //  Server socket will accept connections
     *server = zmq_socket (*ctx, ZMQ_DEALER);
@@ -386,7 +389,8 @@ void shutdown_context_and_server_side (void *ctx,
     close_zero_linger (server);
 
     //  Wait until ZAP handler terminates
-    zmq_threadclose (zap_thread);
+    if (zap_thread)
+      zmq_threadclose (zap_thread);
 
     rc = zmq_ctx_term (ctx);
     assert (rc == 0);