One critical strength of democracy is that it allows voters to remove the current politician - even if that politician would rather not be removed.
Where would you pick your line? Small moves of the line change the size of the disenfranchised group.
And I have to admire your chutzpah of suggesting tests to create a disenfranchised group on an article showing serious flaws with testing... Of course you haven't suggested a single way to fix any flaws. I sincerely hope you are not working in any engineering role.