The point here is not that the tests execution time should dictate the design. On the contrary, the idea of this post was to stress the importance of good design, and that fast tests are just a side effect of it. Now, you might disagree with me on what constitutes good design but that's a different issue.
Don't get me wrong, I agree with the idea that you should look at the root cause of why your tests are slow instead of trying to "fix" the tests. I just feel that what you demonstrated is bad design. So you ended up with bad design and fast tests.
