Refreshing article. We hear so many religious arguments about one side or the other in these days, we really need more of these. I think there's a deep issue t

Refreshing article. We hear so many religious arguments about one side or the other in these days, we really need more of these. I think there's a deep issue that causes all the misunderstanding, the elephant in the room : the definition of a "unit". Words have a meaning in a certain context : if people don't mean the same thing when using the same word they're doomed to misunderstand each other forever. Just ask 5 different people what is a unit and you'll have at least 3 different definitions. The most common one is : in OOP, a unit is a class. From my experience, a unit should be defined as a much higher abstraction level than that. A better definition would be : "a set of use cases that belong to the same module". In other words, unit tests should be we written in a language as close as possible to your domain language. Or : "test your use cases, not your classes". When you do that, you usually write tests for a few major classes that use all your other classes that are just implementation details. This leads to tests that are far more reliable and easy to maintain, because they have very low coupling to the rest of your application. Typically, this means testing classes at the very edge of your app, classes that directly communicate with the end-user, usually services or something like that. Let's say you "unit test" a simple car with a steering module. It has all sorts of internal complex mechanism that IMO you generally don't need to unit test directly. What you need to know is if the business value is correctly delivered to the driver, ie : - when he turns the steering wheel left, does the car turn left - when he brakes, does the car stop - when he presses the gas pedal, does the car accelerates - etc Under the hood there are dozens of other classes that perform actions that you don't really need to care about when you test. They will be tested indirectly anyway, because they're used by the high-level classes you do test. I think many people blindly try to unit test almost all the classes they write and it leads to code duplication all over the place and all sorts of other problems that make projects fail, people angry and think unit tests are bad.