diff --git a/gpio_handler_unittest.h b/gpio_handler_unittest.h
new file mode 100644
index 0000000..5780eaa
--- /dev/null
+++ b/gpio_handler_unittest.h
@@ -0,0 +1,31 @@
+// Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_GPIO_HANDLER_UNITTEST_H__
+#define CHROMEOS_PLATFORM_UPDATE_ENGINE_GPIO_HANDLER_UNITTEST_H__
+
+// This file contains various definitions that are shared by different mock
+// implementations that emulate GPIO behavior in the system.
+
+// Some common strings used by the different cooperating mocks for this module.
+// We use preprocessor constants to allow concatenation at compile-time.
+#define MOCK_GPIO_CHIP_ID     "100"
+#define MOCK_DUTFLAGA_GPIO_ID "101"
+#define MOCK_DUTFLAGB_GPIO_ID "102"
+#define MOCK_SYSFS_PREFIX     "/mock/sys/class/gpio"
+
+namespace chromeos_update_engine {
+
+// Mock GPIO identifiers, used by all mocks involved in unit testing the GPIO
+// module. These represent the GPIOs which the unit tests can cover. They should
+// generally match the GPIOs specified inside GpioHandler.
+enum MockGpioId {
+  kMockGpioIdDutflaga = 0,
+  kMockGpioIdDutflagb,
+  kMockGpioIdMax  // marker, do not remove!
+};
+
+}  // chromeos_update_engine
+
+#endif /* CHROMEOS_PLATFORM_UPDATE_ENGINE_GPIO_HANDLER_UNITTEST_H__ */