Well I don't know what you mean by 'test', but if you want to do something on every node - internal as well as leaf - then something like this:

sub walk
{
    my( $v, @path ) = @_;
    foo( @path );
    if ( keys %$v )
    {
        for my $k ( sort keys %$v )
        {
            walk( $v->{$k}, @path, $k );
        }
    }
}
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If that something might prevent recursion below the current node, then you could have it return a "prune" boolean:

sub walk
{
    my( $v, @path ) = @_;
    foo( @path ) or return; # true means recurse
    if ( keys %$v )
    {
        for my $k ( sort keys %$v )
        {
            walk( $v->{$k}, @path, $k );
        }
    }
}
[download]

Of course, for an even more general solution, you'd want to be able to pass in the "callback":

sub walk
{
    my( $cb, $v, @path ) = @_;
    $cb->( @path ) or return; # true means recurse
    if ( keys %$v )
    {
        for my $k ( sort keys %$v )
        {
            walk( $cb, $v->{$k}, @path, $k );
        }
    }
}
[download]

No doubt someone else will propose an iterator-based solution...