I agree with the general approach suggested in the article (in tests, write/assume the code you wish you had).

But one detail ran counter to my personal practice.

I don't believe that "symmetrical" unit tests are a worthy goal. I believe in testing units of behavior, whether or not they correspond to a method/class. Symmetry leads to brittleness. I refactor as much as possible into private methods, but I leave my tests (mostly) alone. I generally try to have a decent set of acceptance tests, too.

Ideally, you specify a lot of behavior about your public API, but the details are handled in small private methods that are free to change without affecting your tests.