Good article, but doesn't get into any of the problems when doing unit tests. For example, unit testing your UI is a pain in the ass. Unit testing your data access layer that talk to the database is also a huge pain.
Both problems are solvable (MVP design pattern for UIs, frameworks built atop NUnit like Roy Osherove's XTUnit), but they are not addressed in the article. It leaves the reader with a rainbow faery world view of unit testing. The reality is that unit tests are very difficult to write for large sections of code and require much more than the simple examples put forth in the article.
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