Using statement without specific implementation

Question

I have a class which inherits from WebClient - in some code I am trying to test there is the usual:

using(var client = new SomeWebClient()){...}

Now I don't want to use that SomeWebClient class in my tests so I'd like to inject in some kind of stub.

Without using the servicelocator pattern what are my options? I can't use any real IoC as this assembly is used by multiple platforms both mobile and full .NET

I'm sure the answer is staring me in the face but I think I'm having "one of those days"!

Answer 1

1) Use an interface

using(ISomeWebClientc = new SomeWebClient()){...}

2a) Create a factory that returns an ISomeWebClient implementation.

3) Let it return your correct class in the production code or let it create a stub in your tests.

2b) Alternatively, just pass an ISomeWebClient to your class or method and initialize it differently in your test or production code.

Answer 2

You can inject a Func<TResult>. This Func is then called in your using statement, like so:

using (ISomeClient client = InjectedFunc())
{
    ...
}

public delegate Func<ISomeClient> InjectedFunc();

...

Then somewhere in your code you assign this Func a value, which is a code block to be executed later:

InjectedFunc = delegate(){ return new MyImplementation(); };
// or some other way of creating a new instance, as long as
// you return a fresh one

and so, this is functionally the same as if your using block would say:

using (ISomeClient client = new MyImplementation())
{
    ...
}