Let's say I have a complex .NET class, with lots of arrays and other class object members. I need to be able to generate a deep clone of this object - so I write a Clone() method, and implement it with a simple BinaryFormatter serialize/deserialize - or perhaps I do the deep clone using some other technique which is more error prone and I'd like to make sure is tested.

OK, so now (ok, I should have done it first) I'd like write tests which cover the cloning. All the members of the class are private, and my architecture is so good (!) that I haven't needed to write hundreds of public properties or other accessors. The class isn't IComparable or IEquatable, because that's not needed by the application. My unit tests are in a separate assembly to the production code.

What approaches do people take to testing that the cloned object is a good copy? Do you write (or rewrite once you discover the need for the clone) all your unit tests for the class so that they can be invoked with either a 'virgin' object or with a clone of it? How would you test if part of the cloning wasn't deep enough - as this is just the kind of problem which can give hideous-to-find bugs later?