Add a test for process_comment_form().
@todo: continue with that,
and AMP_Comments_Sanitizer::sanitize().

Test more of the method,
including the 'on' value of the form elements.

Improve some of the method descriptions.
And move parent::setUp() to the bottom of setUp().

I deleted some empty lines,
and that moved some lines together.
Those lines need their = to be vertically-aligned.

Remove \ before WP_UnitTestCase.
This test isn't in a namespace,
so it isn't needed.