Tests clearing the selection of a multi-select select element.

On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".

PASS listbox.selectedChildrenCount is 0
PASS listbox.selectedChildrenCount is 1
PASS listbox.selectedChildrenCount is 2
PASS listbox.selectedChildrenCount is 0
PASS successfullyParsed is true

TEST COMPLETE