use Test::More tests => 2;

sub deleteref {
    my $h = shift;
    undef $h;
}

my $c = {d => 3};

deleteref($c);
is( keys %$c, 1,
    'undef on copy of hashref in a subroutine should not clear it' );


undef $c;
is( keys %$c, 0,
    'undef on hash reference, not a copy of it in a subroutine, should clear it' );