How do I test rest service?

http://testwebservices.gov/Service.asmx ... s?City=los angeles&State=ca&Zipcode=&Latitude=&Longitude=&RadiusInMiles=5&NumberOfRecords=&ProviderType=4

When I try to execute this Rest service, it creates a parameter for zipcode, latitude etc, these are nnot required get an error message that I need to enter a value for zipcode when i run the service. Set them as not required does not help, passed a value as =& still does not work, if i delete zipcode the url is incorrect. Please help !!