Added /sub command test

tests/test_cmd_sub.c

@@ -0,0 +1,31 @@
+#include <stdarg.h>
+#include <stddef.h>
+#include <setjmp.h>
+#include <cmocka.h>
+#include <stdlib.h>
+#include <string.h>
+#include <glib.h>
+
+#include "xmpp/xmpp.h"
+#include "xmpp/mock_xmpp.h"
+
+#include "ui/ui.h"
+#include "ui/mock_ui.h"
+
+#include "command/commands.h"
+
+void cmd_sub_shows_message_when_not_connected(void **state)
+{
+    mock_cons_show();
+    CommandHelp *help = malloc(sizeof(CommandHelp));
+    gchar *args[] = { NULL };
+
+    mock_connection_status(JABBER_DISCONNECTED);
+
+    expect_cons_show("You are currently not connected.");
+
+    gboolean result = cmd_sub(args, *help);
+    assert_true(result);
+
+    free(help);
+}