test: Added test for multiselected tabs inside folders, b=no-bug, c=folders, tests

src/zen/folders/ZenFolders.mjs

@@ -320,6 +320,8 @@
       let selectedGroupId = null;
       let itemsAfterSelected = [];
 
+      gBrowser.clearMultiSelectedTabs();
+
       const items = group.childGroupsAndTabs.map((item) => {
         const isSplitView = item.group?.hasAttribute?.('split-view-group');
         const splitGroupId = isSplitView ? item.group.id : null;

src/zen/tests/folders/browser.toml

@@ -14,5 +14,6 @@ support-files = [
 ["browser_folder_density.js"]
 ["browser_folder_max_subfolders.js"]
 ["browser_folder_empty_tab.js"]
+["browser_folder_multiselected.js"]
 
 ["browser_folder_issue_9885.js"]

src/zen/tests/folders/browser_folder_multiselected.js

@@ -0,0 +1,30 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+'use strict';
+
+add_task(async function test_Folder_Multiselected_Tabs() {
+  const selectedTab = gBrowser.selectedTab;
+  const tab1 = BrowserTestUtils.addTab(gBrowser, 'about:blank');
+  const tab2 = BrowserTestUtils.addTab(gBrowser, 'about:blank');
+  const folder = await gZenFolders.createFolder([tab1], {});
+
+  gBrowser.addRangeToMultiSelectedTabs(tab1, tab2);
+  ok(tab1.multiselected, 'Tab 1 should be multiselected');
+  ok(tab2.multiselected, 'Tab 2 should be multiselected');
+  Assert.greater(gBrowser.multiSelectedTabsCount, 1, 'There should be 2 multiselected tabs');
+
+  const collapseEvent = BrowserTestUtils.waitForEvent(window, 'TabGroupCollapse');
+  folder.collapsed = true;
+  await collapseEvent;
+
+  ok(!tab2.multiselected, 'Tab 2 should not be multiselected');
+  Assert.greater(gBrowser.multiSelectedTabsCount, 0, 'There should be 1 multiselected tab');
+
+  for (const t of [tab1, tab2]) {
+    BrowserTestUtils.removeTab(t);
+  }
+
+  gBrowser.selectedTab = selectedTab;
+  await removeFolder(folder);
+});