public void ShouldAsk_ImageProvider_ToGetEachImage()
        {
            var testSrcs = new [] { "blah", "bloo", "bleh" };

            retriever.RetrieveFor(testSrcs);

            foreach (var src in testSrcs)
            {
                provider.AssertWasCalled(p => p.GetImage(src));
            }
        }