diff -r 000000000000 -r 6474c204b198 toolkit/modules/tests/xpcshell/test_NewTabUtils.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/modules/tests/xpcshell/test_NewTabUtils.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,199 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// See also browser/base/content/test/newtab/.
+
+const { classes: Cc, interfaces: Ci, results: Cr, utils: Cu } = Components;
+Cu.import("resource://gre/modules/NewTabUtils.jsm");
+Cu.import("resource://gre/modules/Promise.jsm");
+
+function run_test() {
+  run_next_test();
+}
+
+add_test(function multipleProviders() {
+  // Make each provider generate NewTabUtils.links.maxNumLinks links to check
+  // that no more than maxNumLinks are actually returned in the merged list.
+  let evenLinks = makeLinks(0, 2 * NewTabUtils.links.maxNumLinks, 2);
+  let evenProvider = new TestProvider(done => done(evenLinks));
+  let oddLinks = makeLinks(0, 2 * NewTabUtils.links.maxNumLinks - 1, 2);
+  let oddProvider = new TestProvider(done => done(oddLinks));
+
+  NewTabUtils.initWithoutProviders();
+  NewTabUtils.links.addProvider(evenProvider);
+  NewTabUtils.links.addProvider(oddProvider);
+
+  // This is sync since the providers' getLinks are sync.
+  NewTabUtils.links.populateCache(function () {}, false);
+
+  let links = NewTabUtils.links.getLinks();
+  let expectedLinks = makeLinks(NewTabUtils.links.maxNumLinks,
+                                2 * NewTabUtils.links.maxNumLinks,
+                                1);
+  do_check_eq(links.length, NewTabUtils.links.maxNumLinks);
+  do_check_links(links, expectedLinks);
+
+  NewTabUtils.links.removeProvider(evenProvider);
+  NewTabUtils.links.removeProvider(oddProvider);
+  run_next_test();
+});
+
+add_test(function changeLinks() {
+  let expectedLinks = makeLinks(0, 20, 2);
+  let provider = new TestProvider(done => done(expectedLinks));
+
+  NewTabUtils.initWithoutProviders();
+  NewTabUtils.links.addProvider(provider);
+
+  // This is sync since the provider's getLinks is sync.
+  NewTabUtils.links.populateCache(function () {}, false);
+
+  do_check_links(NewTabUtils.links.getLinks(), expectedLinks);
+
+  // Notify of a new link.
+  let newLink = makeLink(19);
+  expectedLinks.splice(1, 0, newLink);
+  provider.notifyLinkChanged(newLink);
+  do_check_links(NewTabUtils.links.getLinks(), expectedLinks);
+
+  // Notify of a link that's changed sort criteria.
+  newLink.frecency = 17;
+  expectedLinks.splice(1, 1);
+  expectedLinks.splice(2, 0, newLink);
+  provider.notifyLinkChanged({
+    url: newLink.url,
+    frecency: 17,
+  });
+  do_check_links(NewTabUtils.links.getLinks(), expectedLinks);
+
+  // Notify of a link that's changed title.
+  newLink.title = "My frecency is now 17";
+  provider.notifyLinkChanged({
+    url: newLink.url,
+    title: newLink.title,
+  });
+  do_check_links(NewTabUtils.links.getLinks(), expectedLinks);
+
+  // Notify of a new link again, but this time make it overflow maxNumLinks.
+  provider.maxNumLinks = expectedLinks.length;
+  newLink = makeLink(21);
+  expectedLinks.unshift(newLink);
+  expectedLinks.pop();
+  do_check_eq(expectedLinks.length, provider.maxNumLinks); // Sanity check.
+  provider.notifyLinkChanged(newLink);
+  do_check_links(NewTabUtils.links.getLinks(), expectedLinks);
+
+  // Notify of many links changed.
+  expectedLinks = makeLinks(0, 3, 1);
+  provider.notifyManyLinksChanged();
+  // NewTabUtils.links will now repopulate its cache, which is sync since
+  // the provider's getLinks is sync.
+  do_check_links(NewTabUtils.links.getLinks(), expectedLinks);
+
+  NewTabUtils.links.removeProvider(provider);
+  run_next_test();
+});
+
+add_task(function oneProviderAlreadyCached() {
+  let links1 = makeLinks(0, 10, 1);
+  let provider1 = new TestProvider(done => done(links1));
+
+  NewTabUtils.initWithoutProviders();
+  NewTabUtils.links.addProvider(provider1);
+
+  // This is sync since the provider's getLinks is sync.
+  NewTabUtils.links.populateCache(function () {}, false);
+  do_check_links(NewTabUtils.links.getLinks(), links1);
+
+  let links2 = makeLinks(10, 20, 1);
+  let provider2 = new TestProvider(done => done(links2));
+  NewTabUtils.links.addProvider(provider2);
+
+  NewTabUtils.links.populateCache(function () {}, false);
+  do_check_links(NewTabUtils.links.getLinks(), links2.concat(links1));
+
+  NewTabUtils.links.removeProvider(provider1);
+  NewTabUtils.links.removeProvider(provider2);
+});
+
+add_task(function newLowRankedLink() {
+  // Init a provider with 10 links and make its maximum number also 10.
+  let links = makeLinks(0, 10, 1);
+  let provider = new TestProvider(done => done(links));
+  provider.maxNumLinks = links.length;
+
+  NewTabUtils.initWithoutProviders();
+  NewTabUtils.links.addProvider(provider);
+
+  // This is sync since the provider's getLinks is sync.
+  NewTabUtils.links.populateCache(function () {}, false);
+  do_check_links(NewTabUtils.links.getLinks(), links);
+
+  // Notify of a new link that's low-ranked enough not to make the list.
+  let newLink = makeLink(0);
+  provider.notifyLinkChanged(newLink);
+  do_check_links(NewTabUtils.links.getLinks(), links);
+
+  // Notify about the new link's title change.
+  provider.notifyLinkChanged({
+    url: newLink.url,
+    title: "a new title",
+  });
+  do_check_links(NewTabUtils.links.getLinks(), links);
+
+  NewTabUtils.links.removeProvider(provider);
+});
+
+function TestProvider(getLinksFn) {
+  this.getLinks = getLinksFn;
+  this._observers = new Set();
+}
+
+TestProvider.prototype = {
+  addObserver: function (observer) {
+    this._observers.add(observer);
+  },
+  notifyLinkChanged: function (link) {
+    this._notifyObservers("onLinkChanged", link);
+  },
+  notifyManyLinksChanged: function () {
+    this._notifyObservers("onManyLinksChanged");
+  },
+  _notifyObservers: function (observerMethodName, arg) {
+    for (let obs of this._observers) {
+      if (obs[observerMethodName])
+        obs[observerMethodName](this, arg);
+    }
+  },
+};
+
+function do_check_links(actualLinks, expectedLinks) {
+  do_check_true(Array.isArray(actualLinks));
+  do_check_eq(actualLinks.length, expectedLinks.length);
+  for (let i = 0; i < expectedLinks.length; i++) {
+    let expected = expectedLinks[i];
+    let actual = actualLinks[i];
+    do_check_eq(actual.url, expected.url);
+    do_check_eq(actual.title, expected.title);
+    do_check_eq(actual.frecency, expected.frecency);
+    do_check_eq(actual.lastVisitDate, expected.lastVisitDate);
+  }
+}
+
+function makeLinks(frecRangeStart, frecRangeEnd, step) {
+  let links = [];
+  // Remember, links are ordered by frecency descending.
+  for (let i = frecRangeEnd; i > frecRangeStart; i -= step) {
+    links.push(makeLink(i));
+  }
+  return links;
+}
+
+function makeLink(frecency) {
+  return {
+    url: "http://example.com/" + frecency,
+    title: "My frecency is " + frecency,
+    frecency: frecency,
+    lastVisitDate: 0,
+  };
+}