use Test::More;

my @match_wanted = qw( abc bca cab cba bac acb );
my @match_unwanted = qw( aab abbc acc );
sub match {
    my $s = shift;
    return ( ($s =~ /(?:[abc].*){3}/) && ! ($s =~ /([abc]).*\1/) );
}

plan 'tests' => ( scalar @match_wanted + scalar @match_unwanted );

ok( match( $_ ), "matches '$_'" )          for @match_wanted;
ok( ! match( $_ ), "does not match '$_'" ) for @match_unwanted;