Bug 1819980 - Add test for this issue. r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D171651

browser/components/customizableui/test/browser.ini

@@ -129,6 +129,7 @@ skip-if = verify
 tags = overflowable-toolbar
 [browser_addons_area.js]
 [browser_allow_dragging_removable_false.js]
+[browser_bookmarks_empty_message.js]
 [browser_bookmarks_toolbar_collapsed_restore_default.js]
 [browser_bookmarks_toolbar_shown_newtab.js]
 [browser_bootstrapped_custom_toolbar.js]

browser/components/customizableui/test/browser_bookmarks_empty_message.js

@@ -0,0 +1,35 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+add_task(async function empty_message_on_non_empty_bookmarks_toolbar() {
+  await resetCustomization();
+  ok(CustomizableUI.inDefaultState, "Default state to begin");
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.toolbars.bookmarks.visibility", "always"]],
+  });
+
+  CustomizableUI.removeWidgetFromArea("import-button");
+  CustomizableUI.removeWidgetFromArea("personal-bookmarks");
+  CustomizableUI.addWidgetToArea(
+    "bookmarks-menu-button",
+    CustomizableUI.AREA_BOOKMARKS,
+    0
+  );
+
+  let newWin = await BrowserTestUtils.openNewBrowserWindow();
+  let doc = newWin.document;
+  ok(
+    BrowserTestUtils.is_visible(doc.getElementById("PersonalToolbar")),
+    "Personal toolbar should be visible"
+  );
+  ok(
+    doc.getElementById("personal-toolbar-empty").hidden,
+    "Empty message should be hidden"
+  );
+
+  await BrowserTestUtils.closeWindow(newWin);
+  await resetCustomization();
+});