See https://rt.cpan.org/NoAuth/Bugs.html?Dist=Test-Simple plus here's
a few more I haven't put in RT yet.

    Finish (start?) Test::FAQ

    Expand the Test::Tutorial

    $^C exception control?

    Document that everything goes through Test::Builder->ok()

    Add test name to diagnostic output

    Add diag() to details().

    Add at_end() callback?

    Combine all *output methods into outputs().

    Change *output* to return the old FH, not the new one when setting.