What's wrong with

Create Utility Classes and Functions/Methods - For instance, you have a String which is a URL you're passing around (obeying "Use Primitives Wherever Possible"). Create another class with static methods such as isValidUrl(String url)

if the function is a deterministic function (I guess it could be implemented as a simple test against regex) why is is difficult to test? I get that its better to use the system one or your own URL class, but thats really about OO and not testing!