Very preliminary implementation for multiple tests on websocket messages

mytest.t

$t->websocket_ok('/ws')
  ->message_ok
  ->json_message_subtest(sub{
    my ($t, $json) = @_;
    ok $json->[1] >= 0;
    ok $json->[1] <= 3;
  })->finish_ok;

subtest.pm

package Test::Mojo;

use Mojo::JSON 'j';

sub json_message_subtest {
  shift->_message_subtest(shift, 1);
}

sub message_subtest {
  shift->_message_subtest(shift, 0);
}

sub _message_subtest {
  local $Test::Builder::Level = $Test::Builder::Level + 3;
  my ($t, $cb, $is_json) = @_;
  my $msg = $t->message || die "Must call message_ok first"; 
  $t->$cb( $is_json ? j($msg->[1]) : $msg->[1] );
  return $t;
}


# or this, using Test::More::subtest
# message/json is in $_ rather than @_ which this doesn't have access to
sub Test::Mojo::_message_subtest {
  local $Test::Builder::Level = $Test::Builder::Level + 2;

  my ($t, $is_json) = @_;
  my $msg = $t->message || die "Must call message_ok first"; 
  $msg = $is_json ? j($msg->[1]) : $msg->[1];

  my $cb = pop;
  my $name = shift || $is_json ? "JSON message subtest" : "message subtest";

  Test::More->can('subtest')->( $name => $cb ) for $msg; 

  return $t;
}