A technique I used to allow testing code to verify correct object destruction of some classes that use weak references to break cycles was something like:

package Whatever;

sub new {
  my $class = shift;
  my $ob = {};

  # ...

  { our $_total_constructed; $_total_constructed++ }

  bless $ob, $class
}

sub DESTROY { our $_total_destroyed; $_total_destroyed++ }
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The test scripts can then access those package variables and verify that $Whatever::_total_constructed and $Whatever::_total_destroyed are equal at the end of a test run after the last lexical holding an object has gone out of scope.