I've never written a unit test.
I'm reading The art of Unit Testing by Osherove, and he explains a way to choose where to start when you're writing tests for legacy code. Basically you end up with two kinds of tests to write: easy (on components with few dependencies) and hard (on components with many dependencies).
Then he says that starting from the hard ones you have to be more experienced, but that it lets you refactor and make testable a wide part of the system, making later work much easier.
But isn't it true the way around too? I mean, if you start from easy tests, shouldn't you end up making hard tests easier?