I tried the following with my package:
I have importFrom("foo", "bar) in NAMESPACE and removed package "foo" from DESCRIPTION (Imports:).
When checking my package, this is correctly detected, but the error message confused me a bit at first:
"Namespace dependency not required: 'foo'"
I tought: "oh, it is required, why do you tell me otherwise". But then I realised it has to be read "a dependency was detected and it is not mentioned as being required in DESCRIPTION".
So maybe we can improve the message (and its plural form) a bit? E.g.
"Namespace dependency not marked as required (in DESCRIPTION): 'foo'"