MXS-2250 Add test that reveals the problem

Before the MXS-2250 fix, the following ends with an error:

    CREATE TEMPORARY TABLE t (f INT);
    DESCRIBE t;

Reason is that the first is sent to the master (and the table will
not be replicated to slaves) and the latter to some slave.

maxscale-system-test/CMakeLists.txt

@@ -207,6 +207,9 @@ add_test_executable(mxs2167_extra_port.cpp mxs2167_extra_port mxs2167_extra_port
 # Test KILL QUERY functionality
 add_test_executable(kill_query.cpp kill_query replication LABELS REPL_BACKEND)
 
+# MXS-2250: DESCRIBE on temporary table should work.
+add_test_executable(mxs2250_describe_temp_table.cpp mxs2250_describe_temp_table mxs2250_describe_temp_table LABELS REPL_BACKEND)
+
 ############################################
 # BEGIN: Tests that require GTID           #
 ############################################

maxscale-system-test/cnf/maxscale.cnf.template.mxs2250_describe_temp_table

@@ -0,0 +1,61 @@
+[maxscale]
+threads=###threads###
+log_warning=1
+
+[server1]
+type=server
+address=###node_server_IP_1###
+port=###node_server_port_1###
+protocol=mariadbbackend
+
+[server2]
+type=server
+address=###node_server_IP_2###
+port=###node_server_port_2###
+protocol=mariadbbackend
+
+[server3]
+type=server
+address=###node_server_IP_3###
+port=###node_server_port_3###
+protocol=mariadbbackend
+
+[server4]
+type=server
+address=###node_server_IP_4###
+port=###node_server_port_4###
+protocol=mariadbbackend
+
+[Monitor]
+type=monitor
+module=mariadbmon
+servers=server1,server2,server3,server4
+user=maxskysql
+password=skysql
+monitor_interval=1000
+
+[RWS]
+type=service
+router=readwritesplit
+servers=server1,server2,server3,server4
+user=maxskysql
+password=skysql
+slave_selection_criteria=LEAST_ROUTER_CONNECTIONS
+
+[RWS-Listener]
+type=listener
+service=RWS
+protocol=mariadbclient
+port=4006
+#socket=/tmp/rwsplit.sock
+
+[CLI]
+type=service
+router=cli
+
+[CLI Listener]
+type=listener
+service=CLI
+protocol=maxscaled
+#address=localhost
+socket=default

maxscale-system-test/mxs2250_describe_temp_table.cpp

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2019 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2022-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include "mariadb_func.h"
+#include "testconnections.h"
+
+int main(int argc, char* argv[])
+{
+    TestConnections test(argc, argv);
+
+    Connection rwsplit = test.maxscales->rwsplit();
+
+    test.expect(rwsplit.connect(),
+                "Could not connect to rwsplit.");
+    test.expect(rwsplit.query("CREATE TEMPORARY TABLE mxs2250 (a int)"),
+                "Could not create temporary table.");
+    test.expect(rwsplit.query("DESCRIBE mxs2250"),
+                "Could not describe temporary table.");
+
+    return test.global_result;
+}