I found many developers being confused by all the levels of testing in Rails, and some concepts in software testing. Rails community has a very very strong awareness of TDD, and even BDD. Apps are designd using an Outside-in approach, which makes me feel really comfortable and also effective.
In order to do unit testing easier, one should keep a word in mind: Isolation. Try your best to isolate the irrelevant things from your class, and make them easy to config.