ash: Add a unit test for the system update tray item

ash/system/tray_update_unittest.cc

Index: ash/system/tray_update_unittest.cc
diff --git a/ash/system/tray_update_unittest.cc b/ash/system/tray_update_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b32d817bf81fb9653fe2e9a79cc92a6b1ec17914
--- /dev/null
+++ b/ash/system/tray_update_unittest.cc
@@ -0,0 +1,43 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ash/system/tray_update.h"
+
+#include "ash/common/system/tray/system_tray_delegate.h"
+#include "ash/shell.h"
+#include "ash/system/tray/system_tray.h"
+#include "ash/system/tray/system_tray_notifier.h"
+#include "ash/test/ash_test_base.h"
+#include "ash/test/test_system_tray_delegate.h"
+#include "base/macros.h"
+
+namespace ash {
+
+using TrayUpdateTest = test::AshTestBase;
+
+// Tests that the update icon becomes visible when an update becomes
+// available.
+TEST_F(TrayUpdateTest, VisibilityAfterUpdate) {
+  TrayUpdate* tray_update =
+      Shell::GetInstance()->GetPrimarySystemTray()->GetTrayUpdateForTesting();
+
+  // The system starts with no update pending.
+  test::TestSystemTrayDelegate* tray_delegate = GetSystemTrayDelegate();
+  UpdateInfo initial_info;
+  tray_delegate->GetSystemUpdateInfo(&initial_info);
+  EXPECT_FALSE(initial_info.update_required);
+
+  // When no update is pending, the item isn't visible.
+  EXPECT_FALSE(tray_update->tray_view()->visible());
+
+  // Simulate an update.
+  UpdateInfo info;
+  info.update_required = true;
+  Shell::GetInstance()->system_tray_notifier()->NotifyUpdateRecommended(info);
+
+  // Tray item is now visible.
+  EXPECT_TRUE(tray_update->tray_view()->visible());
+}
+
+}  // namespace ash