diff -r 000000000000 -r 6474c204b198 xpcom/tests/TestTextFormatter.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/tests/TestTextFormatter.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <nsTextFormatter.h>
+#include <nsStringGlue.h>
+#include <stdio.h>
+
+int main() 
+{  
+  int test_ok = true;
+
+  nsAutoString fmt(NS_LITERAL_STRING("%3$s %4$S %1$d %2$d %2$d %3$s"));
+  char utf8[] = "Hello"; 
+  char16_t ucs2[]={'W', 'o', 'r', 'l', 'd', 0x4e00, 0xAc00, 0xFF45, 0x0103, 0x00}; 
+  int d=3; 
+
+  char16_t buf[256]; 
+  nsTextFormatter::snprintf(buf, 256, fmt.get(), d, 333, utf8, ucs2); 
+  nsAutoString out(buf); 
+  if(strcmp("Hello World", NS_LossyConvertUTF16toASCII(out).get()))
+    test_ok = false;
+
+  const char16_t *uout = out.get(); 
+  const char16_t expected[] = {0x48, 0x65, 0x6C, 0x6C, 0x6F, 0x20,
+                                0x57, 0x6F, 0x72, 0x6C, 0x64, 0x4E00,
+                                0xAC00, 0xFF45, 0x0103, 0x20, 0x33,
+                                0x20, 0x33, 0x33, 0x33, 0x20, 0x33,
+                                0x33, 0x33, 0x20, 0x48, 0x65, 0x6C,
+                                0x6C, 0x6F};
+  for(uint32_t i=0;i<out.Length();i++) {
+    if(uout[i] != expected[i]) {
+      test_ok = false;
+      break;
+    }
+  }
+  printf(test_ok? "nsTextFormatter: OK\n": "nsTextFormatter: FAIL\n");
+}
+