The API is not intuitive, at least not for me. So, I have to figure out how to return
null with this mocking framework I have never used before.
var service = Substitute.For<ISomethingService>(); // Mock service.Get<IEnumerable<SomeDomain>>(Arg.Any<string>()).ReturnsForAnyArgs(x => null);
Normally, I would just to
.ReturnsForAnyArgs(null), not the case with NSubstitute.