FWIW, this will silence the output, tho using a new Test::Builder object or using Test::Builder::Tester might be the better approach.

use strict;
use warnings;
use Test::More;

my $Test = Test::Builder->new;

sub fail_ok (&;@) {
    my ($code,$description) = @_;

    #  --- silence output
    my $ignore;
    $Test->output(\$ignore);
    $Test->failure_output(\$ignore);
    $Test->todo_output(\$ignore);

    my $result;
  TODO:
    {
        local $TODO= "should be silent";
        #my $result = subtest "Negation of $description", $code;
        my $result = $code->();
    }

    # --- undo silence
    $Test->reset_outputs;

    #  --- output result
    $result
      ? fail($description)
        : pass($description);
}

fail_ok { is(1,2,"") }
  "Bingo! Test failed";


fail_ok { is(1,3,"") }
  "Bingo! Test failed again";

done_testing;
[download]

C:/Perl_524/bin\perl.exe -w d:/exp/pm_negate_test.pl 
ok 2 - Bingo! Test failed
ok 4 - Bingo! Test failed again
1..4
[download]