use warnings
  # FATAL => 'all'
    ;
use strict;


use Test::More
  # tests => ?? + 1  # Test::NoWarnings adds 1 test
    'no_plan'
    ;
use Test::NoWarnings;


my $bases = 'AGCT';
my $agct  = qr{ [\Q$bases\E] }xms;

my ($no_repeat) =
    map qr{ $_ }xms,
    join ' ',
    map { qr{ (?! \Q$_\E $agct* \Q$_\E) }xms }
    split //, $bases
    ;

my $sub_string = qr{ \b $no_repeat $agct{1,4} \b }xms;
my $pair = qr{ $sub_string , $sub_string }xms;


VECTOR:
for my $ar_vector (
    "all the following should be accepted",
    [ 'A,G',        1, '' ],
    [ 'AG,CT',      1, '' ],
    [ 'TC,CA',      1, '' ],
    [ 'GAT,CGA',    1, '' ],
    [ 'CGAT,TG',    1, '' ],
    [ 'CGAT,CTGA',  1, '' ],

    "all the following should be rejected",
    [ '',          0, 'empty string'                              ],
    [ ' ',         0, 'space'                                     ],
    [ ',',         0, 'comma, no sub-strings'                     ],
    [ ',G',        0, 'missing 1st sub-string'                    ],
    [ 'G,',        0, 'missing 2nd sub-string'                    ],
    [ 'ACGT',      0, 'missing comma'                             ],
    [ 'X,A',       0, 'incorrect character'                       ],
    [ 'AA,G',      0, 'repetition of character in 1st substring'  ],
    [ 'ACGTA,G',   0, 'repetition of character in 1st substring'  ],
    [ 'AC,GGC',    0, 'repetition of character in 2nd sub-string' ],
    [ 'AC,ACGTA',  0, 'repetition of character in 2nd sub-string' ],
    [ 'ATGA,TGG',  0, 'repetition in both sub-strings'            ],
    [ 'ATCXG,AAC', 0, 'incorrect character and repetition'        ],

    ) {

    if (not ref $ar_vector) {
        note $ar_vector;
        next VECTOR;
        }

    my ($str, $match, $msg) = @$ar_vector;

    if ($match) {
        ok $str =~ $pair, qq{'$str'};
        }
    else {
        ok $str !~ $pair, qq{'$str': $msg};
        }

    }  # end for VECTOR

##</code><code>##

c:\@Work\Perl\monks\naderra>perl agct_substrings_1.pl
# all the following should be accepted
ok 1 - 'A,G'
ok 2 - 'AG,CT'
ok 3 - 'TC,CA'
ok 4 - 'GAT,CGA'
ok 5 - 'CGAT,TG'
ok 6 - 'CGAT,CTGA'
# all the following should be rejected
ok 7 - '': empty string
ok 8 - ' ': space
ok 9 - ',': comma, no sub-strings
ok 10 - ',G': missing 1st sub-string
ok 11 - 'G,': missing 2nd sub-string
ok 12 - 'ACGT': missing comma
ok 13 - 'X,A': incorrect character
ok 14 - 'AA,G': repetition of character in 1st substring
ok 15 - 'ACGTA,G': repetition of character in 1st substring
ok 16 - 'AC,GGC': repetition of character in 2nd sub-string
ok 17 - 'AC,ACGTA': repetition of character in 2nd sub-string
ok 18 - 'ATGA,TGG': repetition in both sub-strings
ok 19 - 'ATCXG,AAC': incorrect character and repetition
ok 20 - no warnings
1..20