With the explicit approach, you can't conveniently swap the called function for another function unless you do that swap globally:

#use Cwd 'getcwd';
require Cwd;

# use either the stock getcwd()
*getcwd = \&Cwd::getcwd;
print "Locally, with stock getcwd() aliased\n";
which_one();

# Or our fake getcwd(), where we always claim to run under tmp:
*getcwd = sub { "/tmp" };
print "Locally, with stock getcwd() aliased to our fake getcwd()\n";
which_one();
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