refactor: address code review feedback

Makefile.am:
- Replace 4 hardcoded parallel commands with loop over FUNC_TEST_GROUPS
- Easy to extend by adding group numbers to the variable

functionaltests.c:
- Remove test counts from comments (prone to becoming outdated)
- Restore previous comment style with === separators for readability
- Replace switch with groups[] array structure for extensibility

proftest.h:
- Fix comment to describe current state, not the change made

CONTRIBUTING.md:
- Document test groups and parallel execution commands
- Add instructions for adding new test groups

tests/functionaltests/functionaltests.c

@@ -15,17 +15,14 @@
  * functional tests run less frequently than unit tests.
  *
  * Tests are organized into groups for better maintainability and parallel execution:
- *   Group 1: Connect, Ping, Rooms, Software (17 tests)
- *   Group 2: Message, Receipts, Roster, Chat Session (17 tests)
- *   Group 3: Presence (16 tests)
- *   Group 4: MUC, Carbons (19 tests)
+ *   Group 1: Connect, Ping, Rooms, Software
+ *   Group 2: Message, Receipts, Roster, Chat Session
+ *   Group 3: Presence, Disconnect
+ *   Group 4: MUC, Carbons
  *
  * Parallel execution:
  *   ./functionaltests        - run all tests sequentially
- *   ./functionaltests 1      - run group 1 only
- *   ./functionaltests 2      - run group 2 only
- *   ./functionaltests 3      - run group 3 only
- *   ./functionaltests 4      - run group 4 only
+ *   ./functionaltests N      - run group N only (N = 1..num_groups)
  *
  * For parallel execution, run multiple groups simultaneously:
  *   ./functionaltests 1 & ./functionaltests 2 & ./functionaltests 3 & ./functionaltests 4 & wait
@@ -41,6 +38,7 @@
 
 #include "config.h"
 
+#include "common.h"
 #include "proftest.h"
 #include "test_connect.h"
 #include "test_ping.h"
@@ -71,11 +69,12 @@ main(int argc, char* argv[])
         }
     }
 
-    /* GROUP 1: Connect, Ping, Rooms, Software (17 tests)
-     * Basic XMPP session establishment and server queries */
-
-    /* Connection tests - verify login, roster, bookmarks */
+    /* ============================================================
+     * GROUP 1: Connect, Ping, Rooms, Software
+     * Basic XMPP session establishment and server queries
+     * ============================================================ */
     const struct CMUnitTest group1_tests[] = {
+        /* Connection tests - verify login, roster, bookmarks */
         PROF_FUNC_TEST(connect_jid_requests_roster),
         PROF_FUNC_TEST(connect_jid_sends_presence_after_receiving_roster),
         PROF_FUNC_TEST(connect_jid_requests_bookmarks),
@@ -101,10 +100,11 @@ main(int argc, char* argv[])
         PROF_FUNC_TEST(display_software_version_result_in_chat),
     };
 
-    /* GROUP 2: Message, Receipts, Roster, Chat Session (17 tests)
-     * Core messaging and contact management */
+    /* ============================================================
+     * GROUP 2: Message, Receipts, Roster, Chat Session
+     * Core messaging and contact management
+     * ============================================================ */
     const struct CMUnitTest group2_tests[] = {
-
         /* Basic message send/receive */
         PROF_FUNC_TEST(message_send),
         PROF_FUNC_TEST(message_receive_console),
@@ -131,8 +131,10 @@ main(int argc, char* argv[])
         PROF_FUNC_TEST(new_session_when_message_received_from_different_fulljid),
     };
 
-    /* GROUP 3: Presence (16 tests)
-     * Online/away/xa/dnd/chat status management */
+    /* ============================================================
+     * GROUP 3: Presence, Disconnect
+     * Online/away/xa/dnd/chat status management
+     * ============================================================ */
     const struct CMUnitTest group3_tests[] = {
         PROF_FUNC_TEST(presence_online),
         PROF_FUNC_TEST(presence_online_with_message),
@@ -154,10 +156,11 @@ main(int argc, char* argv[])
         PROF_FUNC_TEST(disconnect_ends_session),
     };
 
-    /* GROUP 4: MUC, Carbons (19 tests)
-     * Multi-user chat and message synchronization */
+    /* ============================================================
+     * GROUP 4: MUC, Carbons
+     * Multi-user chat and message synchronization
+     * ============================================================ */
     const struct CMUnitTest group4_tests[] = {
-
         /* MUC room join with various options - XEP-0045 */
         PROF_FUNC_TEST(sends_room_join),
         PROF_FUNC_TEST(sends_room_join_with_nick),
@@ -188,28 +191,31 @@ main(int argc, char* argv[])
         PROF_FUNC_TEST(receive_private_carbon),
     };
 
+    /* Test group registry for easy extension */
+    struct {
+        const char* name;
+        const struct CMUnitTest* tests;
+        size_t count;
+    } 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 4: MUC/Carbons", group4_tests, ARRAY_SIZE(group4_tests) },
+    };
+    const int num_groups = ARRAY_SIZE(groups);
+
     int result = 0;
 
-    switch (group) {
-        case 1:
-            result = cmocka_run_group_tests_name("Group 1: Connect/Ping/Rooms/Software", group1_tests, NULL, NULL);
-            break;
-        case 2:
-            result = cmocka_run_group_tests_name("Group 2: Message/Receipts/Roster/Session", group2_tests, NULL, NULL);
-            break;
-        case 3:
-            result = cmocka_run_group_tests_name("Group 3: Presence", group3_tests, NULL, NULL);
-            break;
-        case 4:
-            result = cmocka_run_group_tests_name("Group 4: MUC/Carbons", group4_tests, NULL, NULL);
-            break;
-        default:
-            /* Run all groups sequentially */
-            result |= cmocka_run_group_tests_name("Group 1: Connect/Ping/Rooms/Software", group1_tests, NULL, NULL);
-            result |= cmocka_run_group_tests_name("Group 2: Message/Receipts/Roster/Session", group2_tests, NULL, NULL);
-            result |= cmocka_run_group_tests_name("Group 3: Presence", group3_tests, NULL, NULL);
-            result |= cmocka_run_group_tests_name("Group 4: MUC/Carbons", group4_tests, NULL, NULL);
-            break;
+    if (group > 0 && group <= num_groups) {
+        /* Run specific group */
+        result = _cmocka_run_group_tests(groups[group - 1].name, groups[group - 1].tests,
+                                         groups[group - 1].count, NULL, NULL);
+    } else {
+        /* Run all groups sequentially */
+        for (int i = 0; i < num_groups; i++) {
+            result |= _cmocka_run_group_tests(groups[i].name, groups[i].tests,
+                                              groups[i].count, NULL, NULL);
+        }
     }
 
     return result;

tests/functionaltests/proftest.h

@@ -2,9 +2,9 @@
 #define __H_PROFTEST
 
 /*
- * XDG paths are now dynamic, generated per-test based on stub_port.
- * This allows parallel test execution without file conflicts.
- * Use xdg_config_home and xdg_data_home variables instead of macros.
+ * XDG paths are dynamic and generated per-test based on stub_port.
+ * Each test instance uses unique directories (./tests/functionaltests/files/{port}/xdg_*)
+ * to allow parallel test execution without file conflicts.
  */
 extern char xdg_config_home[256];
 extern char xdg_data_home[256];