Bug 1892959 - Stub out initial section for backup management within about:preferences. r=backup-reviewers,fluent-reviewers,settings-reviewers,desktop-theme-reviewers,flod,Gijs,kpatenio

Differential Revision: https://phabricator.services.mozilla.com/D209055

browser/components/backup/tests/browser/browser.toml

@@ -0,0 +1,7 @@
+[DEFAULT]
+prefs = [
+  "browser.backup.enabled=true",
+  "browser.backup.preferences.ui.enabled=true",
+]
+
+["browser_preferences.js"]

browser/components/backup/tests/browser/browser_preferences.js

@@ -0,0 +1,40 @@
+/* Any copyright is dedicated to the Public Domain.
+   https://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/**
+ * Tests that the section for controlling backup in about:preferences is
+ * visible, but can also be hidden via a pref.
+ */
+add_task(async function test_preferences_visibility() {
+  await BrowserTestUtils.withNewTab("about:preferences", async browser => {
+    let backupSection =
+      browser.contentDocument.querySelector("#dataBackupGroup");
+    Assert.ok(backupSection, "Found backup preferences section");
+
+    // Our mochitest-browser tests are configured to have the section visible
+    // by default.
+    Assert.ok(
+      BrowserTestUtils.isVisible(backupSection),
+      "Backup section is visible"
+    );
+  });
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.backup.preferences.ui.enabled", false]],
+  });
+
+  await BrowserTestUtils.withNewTab("about:preferences", async browser => {
+    let backupSection =
+      browser.contentDocument.querySelector("#dataBackupGroup");
+    Assert.ok(backupSection, "Found backup preferences section");
+
+    Assert.ok(
+      BrowserTestUtils.isHidden(backupSection),
+      "Backup section is now hidden"
+    );
+  });
+
+  await SpecialPowers.popPrefEnv();
+});