C++ Listview tooltip

I've got a listview in report view that I'm trying to display tooltips for, different per item.

But I can't get any tooltip to be displayed at all...

Here's what I figured out so far:

case LVN_GETINFOTIP:{    LPNMLVGETINFOTIP GetInfoTip = (LPNMLVGETINFOTIP) lParam;    GetInfoTip->pszText = L"TESTING";    // What do I do now? How do I display the tooltip?    return 0;}

After I have received the LVN_GETINFOTIP message, how do I display the tooltip?