Nooobe question - How do I simulate a JSON response?

Hi,

I am developing an app that will make use of a third party API call.  I don't have access to the actual API yet but the team have provided me with the documented paramaterised URL to call and example text file of the JSON response.  I've coded everything up to construct the URL and process the response but cannot 'properly' test it (given API isn't live).  Is there anyway I can simulate the response to the makeWebrequest call/method response using the text file I have?

Thanks