Pointing people only at end-to-end testing seems poor advice. There is value in a mix of all sorts of testing. I agree that testing functionality blows counting

Pointing people only at end-to-end testing seems poor advice. There is value in a mix of all sorts of testing. I agree that testing functionality blows counting coverage by the line out of the water. But since a lot of code that implements algorithms, string manipulation, etc. can be tested just fine with unit tests, and since end-to-end tests are expensive, easily more brittle, require a lot more dependencies, it would be better to have a healthy mix of different types of tests.