1 files changed, 83 insertions, 0 deletions
diff --git a/browser/components/newtab/test/browser/abouthomecache/browser_no_startup_actions.js b/browser/components/newtab/test/browser/abouthomecache/browser_no_startup_actions.js
new file mode 100644
index 0000000000..255b4c9d21
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+++ b/browser/components/newtab/test/browser/abouthomecache/browser_no_startup_actions.js
@@ -0,0 +1,83 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Tests that upon initializing Activity Stream, the cached about:home
+ * document does not process any actions caused by that initialization.
+ * This is because the restored Redux state from the cache should be enough,
+ * and processing any of the initialization messages from Activity Stream
+ * could wipe out that state and cause flicker / unnecessary redraws.
+ */
+add_task(async function test_no_startup_actions() {
+  await withFullyLoadedAboutHome(async browser => {
+    // Make sure we have a cached document. We simulate a restart to ensure
+    // that we start with a cache... that we can then clear without a problem,
+    // before writing a new cache. This ensures that no matter what, we're in a
+    // state where we have a fresh cache, regardless of what's happened in earlier
+    // tests.
+    await simulateRestart(browser);
+    await clearCache();
+    await simulateRestart(browser);
+    await ensureCachedAboutHome(browser);
+
+    // Set up a listener to monitor for actions that get dispatched in the
+    // browser when we fire Activity Stream up again.
+    await SpecialPowers.spawn(browser, [], async () => {
+      let xrayWindow = ChromeUtils.waiveXrays(content);
+      xrayWindow.nonStartupActions = [];
+      xrayWindow.startupActions = [];
+      xrayWindow.RPMAddMessageListener("ActivityStream:MainToContent", msg => {
+        if (msg.data.meta.isStartup) {
+          xrayWindow.startupActions.push(msg.data);
+        } else {
+          xrayWindow.nonStartupActions.push(msg.data);
+        }
+      });
+    });
+
+    // The following two statements seem to be enough to simulate Activity
+    // Stream starting up.
+    AboutNewTab.activityStream.uninit();
+    AboutNewTab.onBrowserReady();
+
+    // Much of Activity Stream initializes asynchronously. This is the easiest way
+    // I could find to ensure that enough of the feeds had initialized to produce
+    // a meaningful cached document.
+    await TestUtils.waitForCondition(() => {
+      let feed = AboutNewTab.activityStream.store.feeds.get(
+        "feeds.discoverystreamfeed"
+      );
+      return feed?.loaded;
+    });
+
+    // Wait an additional few seconds for any other actions to get displayed.
+    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+    await new Promise(resolve => setTimeout(resolve, 2000));
+
+    let [startupActions, nonStartupActions] = await SpecialPowers.spawn(
+      browser,
+      [],
+      async () => {
+        let xrayWindow = ChromeUtils.waiveXrays(content);
+        return [xrayWindow.startupActions, xrayWindow.nonStartupActions];
+      }
+    );
+
+    Assert.ok(!!startupActions.length, "Should have seen startup actions.");
+    info(`Saw ${startupActions.length} startup actions.`);
+
+    Assert.equal(
+      nonStartupActions.length,
+      0,
+      "Should be no non-startup actions."
+    );
+
+    if (nonStartupActions.length) {
+      for (let action of nonStartupActions) {
+        info(`Non-startup action: ${action.type}`);
+      }
+    }
+  });
+});