We keep saying that unit tests are as important as production code. And if we are careful enough with production code as to create the best possible abstraction, why wouldn't we do the same for unit tests?
If the code for unit tests is as important as the main code, then it's definitely wise to design it with extensibility in mind and make it as maintainable as possible. After all, this is the code that will have to be maintained by an engineer other than its original author, so it has to be readable.
The reason why we pay so much attention to make the code's flexibility is that we know requirements change and evolve over time, and eventually as domain business rules change, our code will ...
