use Data::Dumper;
                                                                                
open(IN, "< myfile.txt") or die $!

my $data_ok = 0;
                                                                                
while(<IN>) {
  chomp;
                                                                                
  m/^\s*>\s*$/ and last;       # stop when encountering that last ">".

  $data_ok and push @data, $_; # keep all data inbetween.

  m/Testnok/ and $data_ok = 1; # start after "Testnok".
}
print Dumper \@data;