use strict;
use warnings;

my @array = <DATA>;

foreach my $element (@array) {

    chomp $element;
    my ($fname, $line_number, $content) = split /\s*:\s*/, $element;

    open    my $outfh, '>>', $fname
        or die "Cannot open $fname: $!\n";

    print $outfh $content; # You didn't tell us what is supposed to happen with $line_number.

    close $outfh or die "Couldn't close $fname after writing: $!\n";
}

__DATA__
tests/right/case1: 12 : //comment
tests/right/case1: 13 : //comment
test/right/case3:  5  : //comment