Testing Worldpay URL Params

I'm using PHP and CURL in order to send payment details to worldpay used the hosted integration. I have it working in the test environment but I'm confused about the 'Parameters you can receive' section of the docs. 

I am using the worldpay test environment but I don't see any response parameters when I process a payment - am I missing something?

My site has a 'Pay Now' button that when selected sends the order details to a local PHP file that processes the data as XML and posts it to https://secure-test.worldpay.com/jsp/merchant/xml/paymentService.jsp 

I'm then presented with the hosted payment page where I enter my test card details and a cardholder name of AUTHORISED. The payment is processed and I am redirected to the result URL I specified in my XML file.

I notice the docs state Note: If the MAC is not set, you will only receive the Order Key. I'm not exactly sure what this means or if it applies to the test environment?

I have been reading about securing payments where it states;

Worldpay's redirect message to the result URL contains a number of parameters that include:

orderKey, paymentAmount, paymentCurrency, paymentStatus
A digital signature, called the Message Authentication Code (MAC)

I can't see any of these in the response - any ideas?

Any help is appreciated.