To make it easier to see what keys are bound, you can use the command Get-PSReadlineKeyHandler.
The command Set-PSReadlineKeyHandler also adds support for binding Ctrl-X prefixed commands in Emacs mode.
When the cursor was at the end of the buffer, ShowCompletions would cause an exception trying to move the cursor outside the buffer.
Fixed by writing an explicit newline - done using the native Console api so it isn't redirected by the test framework.
Jason Shirk