NSubstitute HttpPostedFileBase SaveAs - asp.net

Question

On my journey of unit testing my code and I have this code:
var ufile = Substitute.For<HttpPostedFileBase>();
var server = Substitute.For<HttpServerUtilityBase();
var saved = false;
ufile.FileName.Returns("somefileName");
var fileName = fs.Path.GetFileName(ufile.FileName);
var path = fs.Path.Combine(server.MapPath(upath), fileName);
ufile.When(h => h.SaveAs(path)).Do(x => saved = true);
Assert.IsTrue(saved);
So here is what I am testing which I gleaned from different sites:
public ActionResult UploadFiles()
{
var fileinfo = new List<UploadedImageViewModel>();
foreach (string files in Request.Files)
{
var hpf = Request.Files[files] as HttpPostedFileBase; //
if (hpf != null && hpf.ContentLength > 0)
continue;
var FileName = Path.GetFileName(hpf.FileName); //Gets name of file uploaded
var temppath = Path.Combine(Server.MapPath("~/uploadtemp/"), FileName); // creates a string representation of file location
hpf.SaveAs(temppath);
//resize the image before you save it to the right folder under FileUploads
}
return View(fileinfo);
}
Can someone please help me understand this when().Do() syntax of Nsubstitute? In the docs, it says the do should have an action in it but I will need examples to understand.
Then the SaveAs() method of HttpPostedFileBase is void and in Nsubstitute Docs, it says to use when().Do() for void methods so please tell me what is wrong with my unit test.

Answer 1

//Suppose we have this setup
public class MyClass
{
string ReturnSomething()
{
return "FooBar";
}
void DoSomething(out string reason){
reason = 'Oops';
}
}
The usual stubbing syntax for NSubstitute is to use Returns like this:
myClass.ReturnSomething().Returns("wibble");
This stubs out ReturnSomething(), but the Returns syntax only works for methods with a return value.
For methods that have no return we can instead use When().Do(). This is basically what is meant by an Action in their documentation (as opposed to a Func, which does have a return value). A common need to do this is to fill in output parameters on such methods:
string reason;
myClass.When(c => c.DoSomething(out reason))
.Do(args =>
{
args[0] = "Fail";
});
For more on Action and Func see MSDN: Action, Func.
In the specific case of your unit test, instead of setting a variable saved when SaveAs is invoked, consider asserting using the NSubstitute.Received construct instead.