#usr/bin.perl -w 
use strict;

my $file1=<<END;
 test1.tst
 not_run
 test3.tst
 time:2 sec
 test6.tst
 time:2 sec
 test10009.tst
 timeL 39 sec
END

my $file2=<<END;
 test2.tst
 time:3 sec
 test3.tst
 time:6 sec
 test1.tst
time:5 sec
END

open FILE1, '<', \$file1 or die "cannot open file1 $!";
open FILE2, '<', \$file2 or die "cannot open file2 $!";

my %seenFile1;
while (<FILE1>)
{
    my ($file_name) = $_ =~ (/^\s*(test\d\.tst)\s*/);
    $seenFile1{$file_name} = 1 if $file_name;
}
close FILE1;

my @common;

while (<FILE2>)
{
    my ($file_name) = $_ =~ (/^\s*(test\d\.tst)\s*/);
    #as OP wants, save common names for other uses....
    #
    push @common, $file_name  if $seenFile1{$file_name};
}

#one use is sort
#

foreach (sort {my ($Anum) = $a =~ /(\d+)/;  
               my ($Bnum) = $b =~ /(\d+)/;
                    $Anum <=> $Bnum
               }@common
        )
{
   print "$_\n";
}

__END__
test1.tst
test3.tst