Unit tests for simple REST client [duplicate] - rest

Question

This question already has answers here:
Need some advice for trying to mock a .NET WebClient or equivalent
(2 answers)
Closed 6 years ago.
Let's assumed that i've got simple method which gets some data from REST service. Method looks like:
public string GetDataFromRest(string uri) {
string result = String.Empty;
using(WebClient web = new WebClient()) {
result = web.DownloadString(uri);
}
return result;
}
So, now i want to create unit test for this method. I don't want to use external REST service but i want fake response from any URI without real conecting to service. Something like every execute of GetDataFromRest(uri) in Unit Test -> always returns some XML.

Answer 1

As the posted answer goes into some detail, part of your problem is you have a dependency on the WebClient class.
A sample wrapper for WebClient could look like:
public interface IWebClient
{
string DownloadString(string address);
}
public class WebClientWrapper : IWebClient
{
public string DownloadString(string address)
{
using(WebClient web = new WebClient()) {
return result = web.DownloadString(uri);
}
}
}
public class MyClass
{
private readonly IWebClient _webClient;
public MyClass(IWebClient webClient)
{
_webClient = webClient;
}
public string GetDataFromRest(string uri)
{
return _webClient.DownloadString(uri);
}
}
Now of course going this route means WebClientWrapper can be unit tested with a "less real" URI or what that you specifically control. I've only implemented one method of the WebClient, but this externalizes the dependency within GetDataFromRest from a real URI, as you can now mock the return data. This also helps in that anything else you need a WebClient for, you can now use the wrapper class, and easily mock the returned data, as you are now programming to an interface, rather than a concretion.