Agile Web Development with Rails 7: Add a warning concerning `has_no_field' (PDF B3.0 p. 185, 186)

I think a hint about being extra careful when using has_no_field may be useful.

I’ve seen projects where this particular check passed, when is shouldn’t have: ‘Routing number’ and ‘Routing number’ look identical, but actually aren’t. — Checking that a certain text is not present is true for nearly all possible texts, after all.