diff -r 000000000000 -r 6474c204b198 xpcom/tests/TestObserverService.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/tests/TestObserverService.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,152 @@
+/* -*- 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 "nsISupports.h"
+#include "nsIComponentManager.h"
+#include "nsIObserverService.h"
+#include "nsIObserver.h"
+#include "nsISimpleEnumerator.h"
+#include "nsStringGlue.h"
+#include "nsWeakReference.h"
+#include "nsComponentManagerUtils.h"
+#include "mozilla/Attributes.h"
+
+#include <stdio.h>
+
+static nsIObserverService *anObserverService = nullptr;
+
+static void testResult( nsresult rv ) {
+    if ( NS_SUCCEEDED( rv ) ) {
+        printf("...ok\n");
+    } else {
+        printf("...failed, rv=0x%x\n", (int)rv);
+    }
+    return;
+}
+
+void printString(nsString &str) {
+    printf("%s", NS_ConvertUTF16toUTF8(str).get());
+}
+
+class TestObserver MOZ_FINAL : public nsIObserver,
+                               public nsSupportsWeakReference
+{
+public:
+    TestObserver( const nsAString &name )
+        : mName( name ) {
+    }
+    NS_DECL_ISUPPORTS
+    NS_DECL_NSIOBSERVER
+
+    nsString mName;
+
+private:
+    ~TestObserver() {}
+};
+
+NS_IMPL_ISUPPORTS( TestObserver, nsIObserver, nsISupportsWeakReference )
+
+NS_IMETHODIMP
+TestObserver::Observe( nsISupports     *aSubject,
+                       const char *aTopic,
+                       const char16_t *someData ) {
+    nsCString topic( aTopic );
+    nsString data( someData );
+    	/*
+    		The annoying double-cast below is to work around an annoying bug in
+    		the compiler currently used on wensleydale.  This is a test.
+    	*/
+    printString(mName);
+    printf(" has observed something: subject@%p", (void*)aSubject);
+    printf(" name=");
+    printString(reinterpret_cast<TestObserver*>(reinterpret_cast<void*>(aSubject))->mName);
+    printf(" aTopic=%s", topic.get());
+    printf(" someData=");
+    printString(data);
+    printf("\n");
+    return NS_OK;
+}
+
+int main(int argc, char *argv[])
+{
+    nsCString topicA; topicA.Assign( "topic-A" );
+    nsCString topicB; topicB.Assign( "topic-B" );
+    nsresult rv;
+
+    nsresult res = CallCreateInstance("@mozilla.org/observer-service;1", &anObserverService);
+	
+    if (res == NS_OK) {
+
+        nsIObserver *aObserver = new TestObserver(NS_LITERAL_STRING("Observer-A"));
+        aObserver->AddRef();
+        nsIObserver *bObserver = new TestObserver(NS_LITERAL_STRING("Observer-B"));
+        bObserver->AddRef();
+            
+        printf("Adding Observer-A as observer of topic-A...\n");
+        rv = anObserverService->AddObserver(aObserver, topicA.get(), false);
+        testResult(rv);
+ 
+        printf("Adding Observer-B as observer of topic-A...\n");
+        rv = anObserverService->AddObserver(bObserver, topicA.get(), false);
+        testResult(rv);
+ 
+        printf("Adding Observer-B as observer of topic-B...\n");
+        rv = anObserverService->AddObserver(bObserver, topicB.get(), false);
+        testResult(rv);
+
+        printf("Testing Notify(observer-A, topic-A)...\n");
+        rv = anObserverService->NotifyObservers( aObserver,
+                                   topicA.get(),
+                                   MOZ_UTF16("Testing Notify(observer-A, topic-A)") );
+        testResult(rv);
+
+        printf("Testing Notify(observer-B, topic-B)...\n");
+        rv = anObserverService->NotifyObservers( bObserver,
+                                   topicB.get(),
+                                   MOZ_UTF16("Testing Notify(observer-B, topic-B)") );
+        testResult(rv);
+ 
+        printf("Testing EnumerateObserverList (for topic-A)...\n");
+        nsCOMPtr<nsISimpleEnumerator> e;
+        rv = anObserverService->EnumerateObservers(topicA.get(), getter_AddRefs(e));
+
+        testResult(rv);
+
+        printf("Enumerating observers of topic-A...\n");
+        if ( e ) {
+          nsCOMPtr<nsIObserver> observer;
+          bool loop = true;
+          while( NS_SUCCEEDED(e->HasMoreElements(&loop)) && loop) 
+          {
+              nsCOMPtr<nsISupports> supports;
+              e->GetNext(getter_AddRefs(supports));
+              observer = do_QueryInterface(supports);
+              printf("Calling observe on enumerated observer ");
+              printString(reinterpret_cast<TestObserver*>
+                                          (reinterpret_cast<void*>(observer.get()))->mName);
+              printf("...\n");
+              rv = observer->Observe( observer, 
+                                      topicA.get(), 
+                                      MOZ_UTF16("during enumeration") );
+              testResult(rv);
+          }
+        }
+        printf("...done enumerating observers of topic-A\n");
+
+        printf("Removing Observer-A...\n");
+        rv = anObserverService->RemoveObserver(aObserver, topicA.get());
+        testResult(rv);
+
+
+        printf("Removing Observer-B (topic-A)...\n");
+        rv = anObserverService->RemoveObserver(bObserver, topicB.get());
+        testResult(rv);
+        printf("Removing Observer-B (topic-B)...\n");
+        rv = anObserverService->RemoveObserver(bObserver, topicA.get());
+        testResult(rv);
+       
+    }
+    return 0;
+}