如何在单元测试

Question

     public class PrintScreen : Window
    {
            public override void OnApplyTemplate()
            {
                base.OnApplyTemplate();
                IntPtr      handle = new WindowInteropHelper(this).Handle;
                if (handle != (IntPtr)0) // can happen in unit tests
                {
                    src = HwndSource.FromHwnd(handle);
                    src.AddHook(WindowsMsgHook);
                    RegisterPrintScreenKeyStroke();
                }
            }

            // Register the Alt+PrintScreen hot key.
            private void RegisterPrintScreenKeyStroke()
            {
                if(printScreenHKey == null)
                {
                    printScreenHKey = new HotKey();
                    printScreenHKey.Modifier = ModifierKeys.Alt;
                    printScreenHKey.Key = Forms.Keys.PrintScreen;
                    printScreenHKey.ToRegisterHotKey();
                }
            }


            private IntPtr WindowsMsgHook( IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
            {

                // Checks whether the window message is hotkey message. 
                if(msg == WM_HOTKEY)
                {
                    //The high-order word specifies the virtual key code of the hot key.
                    int vkey = (((int)lParam >> 16) & 0xFFFF);
                    if (!handled && vkey == (uint)Forms.Keys.PrintScreen)
                    {
                        handled = true;
                        PrintScreenPressed();
                    }
                }
                return (IntPtr)0;
            }

    public const int WM_HOTKEY = 0x0312;

    }

我编写了一个代码来截取主屏幕的截图，该主屏幕使用窗口的句柄来注册热键。现在，我想编写单元测试来测试这段代码。你能给出写UT的想法。

热键是另一个类。

公共类HotKey                     {

                    public HotKey()
                    {
                        winHandle = this.Instance.Handle;
                        winHashCode = this.Instance.GetType().GetHashCode();
                    }
                   public System.Windows.Input.ModifierKeys Modifier { get; set; }
                   public System.Windows.Forms.Keys Key { get; set; }

                    ///<summary>
                    /// Method uses User32 API function to register hot keystrokes.
                    ///</summary>
                    public void ToRegisterHotKey()
                    {
                        ToUnregisterHotKey();
                        if (!isRegistered && winHandle != IntPtr.Zero)
                        {
                            if (RegisterHotKey(winHandle, winHashCode,(uint)Modifier, (uint)Key))
                            {
                                isRegistered = true;
                            }
                        }
                    }

                    public void ToUnregisterHotKey()
                    {
                        if (isRegistered && winHandle != IntPtr.Zero)
                        {
                            if (!UnregisterHotKey(winHandle, winHashCode))
                               //Error logging
                            isRegistered = false;
                        }
                    }

                    [DllImport("user32.dll")]
                    private static extern bool RegisterHotKey(IntPtr wndHandle, int id, uint modifier, uint key);
                    [DllImport("user32.dll")]
                    private static extern bool UnregisterHotKey(IntPtr hWnd, int id);
                    private IntPtr winHandle;
                    private int winHashCode; 
                    private bool isRegistered;
        }