Issue 4223 - Adapt notification tests to work in adblockpluscore repository

test/stub-modules/prefs.js

-exports.Prefs = {
+let listeners = [];
+
+let Prefs = exports.Prefs = {
+  enabled: true,
   savestats: true,
   subscriptions_autoupdate: true,
   subscriptions_fallbackerrors: 5,
-  subscriptions_fallbackurl: ""
+  subscriptions_fallbackurl: "",
+  notificationurl: "http://example.com/notification.json",
+  notificationdata: {},
+  notifications_ignoredcategories: []
 };
+
+for (let key of Object.keys(Prefs))
+{
+  let value = Prefs[key];
+  Object.defineProperty(Prefs, key, {
+    get: () => value,
+    set: newValue =>
+    {
+      if (newValue == value)
+        return;
+
+      value = newValue;
+      for (let listener of listeners)
+        listener(key);
+    }
+  });
+}
+
+Prefs.addListener = function(listener)
+{
+  if (listeners.indexOf(listener) < 0)
+    listeners.push(listener);
+};
+
+Prefs.removeListener = function(listener)
+{
+  let index = listeners.indexOf(listener);
+  if (index >= 0)
+    listeners.splice(index, 1);
+};