{
  package A;
  local *x = sub { die "aaa" };
 
  #run tests
  ...
}
# &x reset after leaving block

##</code><code>##

$old_coderef = \&x;
 
# run tests
... # do what you want 
... # (but think about the omen ;-)
 
*x = $old_coderef;