my $res = '';
for my $i ( 0 .. (length($array_of_test_names[0]) -1)) {
	my $letter = substr ($array_of_test_names[0],$i,1);
	last if ( scalar grep { $letter ne substr($array_of_test_names[$_],$i,1)} (0 .. $#array_of_test_names));
	$res .= $letter;
};
print $res,"\n";