sub command_output ( ... ) {
    subtest $test_name => sub {
        my $output = _run_command( $command, $args );

        return subtest ... if 'CODE' eq ref $test;
        return like ... if 'Regexp' eq ref $test;
        return is ...;
    };
}

sub _run_command ( $command, $args ) {
    # start command and retrieve output
    return $output
}