TDD in Objective-c: property/constructor injection or method swizzling?

Since I've started using TDD I've been firmly convinced that it's a great way to write good correct pattern compliant code, without forcing my design decisions. And I found this true in 80% scenarios, but I have problems when it comes to test certain tipe of objects which, for some reason, wrap and hide an object inside the implementation.

To give you an example let's think of a MyLocationManager objects which gives a common interface to my objects to be used, and wraps inside an NSLocationManager. When I want to test such an object I have to supply a mock NSLocationManager of course.

I have of course the property/constructor injection method, but this means adding a property, or a constructor parameter, with an objects that I simply want to hide from the other objects: I've created MyLocationManager to wrap and hide NSLocationManager, why should I be exposing a property just to test it?

A method I've found which is pretty straightforward is to method swizzle NSLocationManager's methods, so I can exchange the actual implementation of a method with a mock one, but this seems pretty unclean and I don't know how safe it is.

As far as I can understand, there might be a Demeter Law's violation in not exposing a property constructor, but on the other hand, I think that in objective-c some flexibility on this pattern is accepted.

So my question is, there should be any way I'm not clearly seeing to adopt property/constructor injection, or method swizzling is a commonly used practice?

Are there any other techniques for this scenario adopted that I should better use?

On a footnote: This problem is true even with objects that wraps networking code and classes like NSUrlSession.