How to manually trigger an downarrow keyboard event in Monaco Editor?

I'm in charge of testing (with selenium) a Monaco editor field in our webapp. I know how to trigger the completions dropdown with:

editor.trigger('', 'editor.action.triggerSuggest')

But the completion list is big and I'd like to navigate in this list by using the downarrow key. How can I fire this event? I tried with no luck:

editor.trigger('', 'type', monaco.KeyCode.DownArrow)

Thank you.