Added carbons command functional test

tests/functionaltests/test_carbons.c

@@ -0,0 +1,24 @@
+#include <glib.h>
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <stabber.h>
+#include <expect.h>
+
+#include "proftest.h"
+
+void
+send_enable_carbons(void **state)
+{
+    prof_connect();
+
+    prof_input("/carbons on");
+
+    assert_true(stbbr_received(
+        "<iq id=\"*\" type=\"set\"><enable xmlns=\"urn:xmpp:carbons:2\"/></iq>"
+    ));
+}