Extend Selection After Double Click

This tests modifying a selection created with a double click with shift arrow key.

This test does not run interactively. It uses the event sender to do mouse clicks. To run it manually, double click on the blue "g", then press shift-left-arrow twice. Then repeat those steps again. The selection should include the words "a paragraph" on mac and "paragra" on win/linux..

This is a paragraph.