diff -r 000000000000 -r 6474c204b198 xpcom/tests/TestCRT.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/tests/TestCRT.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,98 @@
+/* -*- Mode: C++; tab-width: 2; 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 "nsCRT.h"
+#include "nsString.h"
+#include "plstr.h"
+#include <stdlib.h>
+
+namespace TestCRT {
+
+// The return from strcmp etc is only defined to be postive, zero or
+// negative. The magnitude of a non-zero return is irrelevant.
+int sign(int val) {
+    if (val == 0)
+	return 0;
+    else {
+	if (val > 0)
+	    return 1;
+	else
+	    return -1;
+    }
+}
+
+
+// Verify that nsCRT versions of string comparison routines get the
+// same answers as the native non-unicode versions. We only pass in
+// iso-latin-1 strings, so the comparison must be valid.
+static void Check(const char* s1, const char* s2, int n)
+{
+#ifdef DEBUG
+  int clib =
+#endif
+    PL_strcmp(s1, s2);
+
+#ifdef DEBUG
+  int clib_n =
+#endif
+    PL_strncmp(s1, s2, n);
+
+  nsAutoString t1,t2; 
+  t1.AssignWithConversion(s1);
+  t2.AssignWithConversion(s2);
+  const char16_t* us1 = t1.get();
+  const char16_t* us2 = t2.get();
+
+#ifdef DEBUG
+  int u2 =
+#endif
+    nsCRT::strcmp(us1, us2);
+
+#ifdef DEBUG
+  int u2_n =
+#endif
+    nsCRT::strncmp(us1, us2, n);
+
+  NS_ASSERTION(sign(clib) == sign(u2), "strcmp");
+  NS_ASSERTION(sign(clib_n) == sign(u2_n), "strncmp");
+}
+
+struct Test {
+  const char* s1;
+  const char* s2;
+  int n;
+};
+
+static Test tests[] = {
+  { "foo", "foo", 3 },
+  { "foo", "fo", 3 },
+
+  { "foo", "bar", 3 },
+  { "foo", "ba", 3 },
+
+  { "foo", "zap", 3 },
+  { "foo", "za", 3 },
+
+  { "bar", "foo", 3 },
+  { "bar", "fo", 3 },
+
+  { "bar", "foo", 3 },
+  { "bar", "fo", 3 },
+};
+#define NUM_TESTS int((sizeof(tests) / sizeof(tests[0])))
+
+}
+
+using namespace TestCRT;
+
+int main()
+{
+  Test* tp = tests;
+  for (int i = 0; i < NUM_TESTS; i++, tp++) {
+    Check(tp->s1, tp->s2, tp->n);
+  }
+
+  return 0;
+}