diff --git a/mozilla/base/tests/TestAutoLock.cpp b/mozilla/base/tests/TestAutoLock.cpp
new file mode 100644
index 00000000000..152f51e9da9
--- /dev/null
+++ b/mozilla/base/tests/TestAutoLock.cpp
@@ -0,0 +1,72 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ *
+ * The contents of this file are subject to the Netscape Public License
+ * Version 1.0 (the "NPL"); you may not use this file except in
+ * compliance with the NPL.  You may obtain a copy of the NPL at
+ * http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the NPL is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
+ * for the specific language governing rights and limitations under the
+ * NPL.
+ *
+ * The Initial Developer of this code under the NPL is Netscape
+ * Communications Corporation.  Portions created by Netscape are
+ * Copyright (C) 1998 Netscape Communications Corporation.  All Rights
+ * Reserved.
+ */
+
+/*
+
+  Some tests for nsAutoLock.
+
+ */
+
+#include "nsAutoLock.h"
+#include "prthread.h"
+
+PRLock* gLock;
+int gCount;
+
+static void run(void* arg)
+{
+    for (int i = 0; i < 1000000; ++i) {
+        nsAutoLock guard(gLock);
+        ++gCount;
+        PR_ASSERT(gCount == 1);
+        --gCount;
+    }
+}
+
+
+int main(int argc, char** argv)
+{
+    gLock = PR_NewLock();
+    gCount = 0;
+
+    // This shouldn't compile
+    //nsAutoLock* l1 = new nsAutoLock(theLock);
+    //delete l1;
+
+    // Create a block-scoped lock. This should compile.
+    {
+        nsAutoLock l2(gLock);
+    }
+
+    // Fork a thread to access the shared variable in a tight loop
+    PRThread* t1 =
+        PR_CreateThread(PR_SYSTEM_THREAD,
+                        run,
+                        nsnull,
+                        PR_PRIORITY_NORMAL,
+                        PR_GLOBAL_THREAD,
+                        PR_JOINABLE_THREAD,
+                        0);
+
+    // ...and now do the same thing ourselves
+    run(nsnull);
+
+    // Wait for the background thread to finish, if necessary.
+    PR_JoinThread(t1);
+    return 0;
+}
diff --git a/mozilla/xpcom/tests/TestAutoLock.cpp b/mozilla/xpcom/tests/TestAutoLock.cpp
new file mode 100644
index 00000000000..152f51e9da9
--- /dev/null
+++ b/mozilla/xpcom/tests/TestAutoLock.cpp
@@ -0,0 +1,72 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ *
+ * The contents of this file are subject to the Netscape Public License
+ * Version 1.0 (the "NPL"); you may not use this file except in
+ * compliance with the NPL.  You may obtain a copy of the NPL at
+ * http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the NPL is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
+ * for the specific language governing rights and limitations under the
+ * NPL.
+ *
+ * The Initial Developer of this code under the NPL is Netscape
+ * Communications Corporation.  Portions created by Netscape are
+ * Copyright (C) 1998 Netscape Communications Corporation.  All Rights
+ * Reserved.
+ */
+
+/*
+
+  Some tests for nsAutoLock.
+
+ */
+
+#include "nsAutoLock.h"
+#include "prthread.h"
+
+PRLock* gLock;
+int gCount;
+
+static void run(void* arg)
+{
+    for (int i = 0; i < 1000000; ++i) {
+        nsAutoLock guard(gLock);
+        ++gCount;
+        PR_ASSERT(gCount == 1);
+        --gCount;
+    }
+}
+
+
+int main(int argc, char** argv)
+{
+    gLock = PR_NewLock();
+    gCount = 0;
+
+    // This shouldn't compile
+    //nsAutoLock* l1 = new nsAutoLock(theLock);
+    //delete l1;
+
+    // Create a block-scoped lock. This should compile.
+    {
+        nsAutoLock l2(gLock);
+    }
+
+    // Fork a thread to access the shared variable in a tight loop
+    PRThread* t1 =
+        PR_CreateThread(PR_SYSTEM_THREAD,
+                        run,
+                        nsnull,
+                        PR_PRIORITY_NORMAL,
+                        PR_GLOBAL_THREAD,
+                        PR_JOINABLE_THREAD,
+                        0);
+
+    // ...and now do the same thing ourselves
+    run(nsnull);
+
+    // Wait for the background thread to finish, if necessary.
+    PR_JoinThread(t1);
+    return 0;
+}