You can still override the things:

package X;
use strict;
use Exporter 'import';
use vars '@EXPORT_OK';
@EXPORT_OK = qw(func1 func2 );
sub func1 { ... };
sub func2 { ... };

sub should_stop { ... };

until (should_stop()){...}
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And then in your test file:

local *X::should_stop = sub { return 1 };
require X;
X->import('func1');
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