Try URI::Find. It is a little tricky though:

use strict;
use URI::Find;
# Time passes
sub test_uri {
  my $val = shift;
  my $copy = $val;
  my $found;
  find_uris($copy, sub {
      $found = shift;
    }
  );
  return $val eq $found;
}
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Note that this test is also rather picky...you may prefer to do the following which is both simpler and more useful IMO:

sub normalize_uri {
  my $found;
  find_uris($val, sub {
      $found = shift;
    }
  );
  return $found;
}
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If the text is even remotely acceptable, it will try to guess at something valid... :-)