test(disco): add functional test for disco#items error handling

Verifies that /disco items displays error responses (e.g. service-unavailable)
to the user, per XEP-0030 Section 7.

tests/functionaltests/functionaltests.c

@@ -53,6 +53,7 @@
 #include "test_muc.h"
 #include "test_disconnect.h"
 #include "test_lastactivity.h"
+#include "test_disco.h"
 
 /* Macro to wrap each test with setup/teardown functions */
 #define PROF_FUNC_TEST(test) cmocka_unit_test_setup_teardown(test, init_prof_test, close_prof_test)
@@ -143,7 +144,7 @@ main(int argc, char* argv[])
     };
 
     /* ============================================================
-     * GROUP 3: Presence, Disconnect
+     * GROUP 3: Presence, Disconnect, Disco
      * Online/away/xa/dnd/chat status management
      * ============================================================ */
     const struct CMUnitTest group3_tests[] = {
@@ -165,6 +166,9 @@ main(int argc, char* argv[])
 
         /* Disconnect - clean session termination */
         PROF_FUNC_TEST(disconnect_ends_session),
+
+        /* Service Discovery - XEP-0030 */
+        PROF_FUNC_TEST(disco_items_error_handling),
     };
 
     /* ============================================================
@@ -214,7 +218,7 @@ main(int argc, char* argv[])
     } groups[] = {
         { "Group 1: Connect/Ping/Rooms/Software", group1_tests, ARRAY_SIZE(group1_tests) },
         { "Group 2: Message/Receipts/Roster/Session", group2_tests, ARRAY_SIZE(group2_tests) },
-        { "Group 3: Presence/Disconnect", group3_tests, ARRAY_SIZE(group3_tests) },
+        { "Group 3: Presence/Disconnect/Disco", group3_tests, ARRAY_SIZE(group3_tests) },
         { "Group 4: MUC/Carbons", group4_tests, ARRAY_SIZE(group4_tests) },
     };
     const int num_groups = ARRAY_SIZE(groups);