sub list_tests {
    my $class = ref($_[0]) || $_[0];
    my @tests;
    no strict 'refs';
    if (defined(@{"$class\::TESTS"})) {
        push @tests, @{"$class\::TESTS"};
    }
    else {
        push @tests, grep { /^test/ && $class->can($_) }
            keys %{"$class\::"};
    }
    push @tests, map {$_->can('list_tests') ? $_->list_tests : ()}
        @{"$class\::ISA"};
    my %tests = map {$_ => ''} @tests if @tests;
    return keys %tests;
}