Unit testing an object in Perl. Checking that it contains specific hash values

I have created an error object from an error hash and I'm trying to create unit tests that check the objects contain all the correct keys.

ErrorLibrary.pm

use constant {

    CABLING_ERROR => {
    errorCode => 561,
    message => "cabling is not correct at T1",
    tt => { template => 'disabled'},
    fatal => 1,
    link =>'http://ift.tt/231CJxl',
    },
};

Error.pm - new subroutine. (Takes error hash as arg & creates a new error object)

package ASC::Builder:Error;
sub new {

    my ($package, $first_param) = (shift, shift);


    if (ref $first_param eq 'HASH') {
        my %params = @_;
        return bless { message => $first_param->{message}, %params}, $package;
    }
    else {
        my %params = @_; 
        return bless {message => $first_param, %params}, $package;

}   
}

I'm not sure what I should be testing as my expected output. The specific message key in the hash or an Error object itself. I've been trying to test if a certain key of the hash is contained in the error object, but I don't think I'm going about it the right way. Anyway here is what I've been messing around with:

error_test.t

my $error = CABLING_ERROR;
#is(ref $error, 'HASH', 'error is a hashref');


my $error_in = ASC::Builder::Error->new($error);

my $exp_out_A = ($error->{message}); # is this the right expected output????

is(ref $error_in eq ASC::Builder::Error, 'It is an Error object'); #seen something like this online

#is(defined $error->{errorCode}, 1, "Error object contains key errorCode"); #these only test that the error hash contains these keys
#is(defined $error->{message}, 1, "Error object contains key message");


is($error_in, $exp_out_A, 'Correct message output');

The test file is a bit messy, just because I've been trying various attempts. I hope all the code is free of syntax errors :). Any help would be much appreciated!