In a new post to his site Matthias Noback takes a look at unit testing your code and how it can be "dangerous" if you use mocking/doubles in the wrong way (not effective testing). Instead, he makes the recommendation to mock at architectural boundaries, specifically looking at mocking persistence and time handling.
More and more I've come to realize that I've been mocking less and less. The thing is, creating test doubles is a very dangerous activity.
[...] For example, by creating a test double for the EntityManager, we're assuming that it will work well with any objects we'll pass to it. If you've ever debugged an issue with an EntityManager, you know that this is a bad assumption. Anything may go wrong: a mistake in the mapping, missing configuration for cascading persist/delete behavior, an issue with the database credentials, availability of the database server, network connectivity, a missing or invalid database schema, etc.
He then gets into the concepts behind mocking across the "architecturally significant boundaries" and what kind of functionality this involves. He then gets into the two different examples sharing some of the basic concepts and test examples for evaluating persistence and time handling. He finishes up with a look at some of the potential consequences ("outcomes" is really a better word) of refactoring your tests and code to follow these ideas.
