ken@titan ~/tmp/pm_11152777_test_stdin/t
$ cat test_json.t
#!perl

use strict;
use warnings;
use autodie;

use Cwd 'abs_path';
use File::Basename 'dirname';
my $THISDIR;
BEGIN { $THISDIR = dirname abs_path __FILE__ }

use JSON::MaybeXS;
use POSIX '_exit';
use Test::More;

my @file_bases = qw{test1 testA};
plan tests => 0+@file_bases;

for my $file_base (@file_bases) {
    my $json_data = '';
    my $child_pid = open my $from_kid, '-|';

    if ($child_pid) {
        # parent process (pipe from child):
        #   reads JSON from "effective" STDIN
        while (my $line = <$from_kid>) {
            $json_data .= $line;
        }

        waitpid $child_pid, 0;
    }
    else {
        # child process (pipe to parent):
        #   writes JSON to STDOUT
        my $json_file = "$THISDIR/../data/$file_base.json";
        open my $json_fh, '<', $json_file;

        while (my $line = <$json_fh>) {
            print $line;
        }

        _exit 0;
    }

    my $perl_data = decode_json($json_data);
    my $reference_data = do "$THISDIR/../data/$file_base.perl";
    is_deeply $perl_data, $reference_data, "Testing '$file_base'";
}