The note is the purpose of this PR. If it's not informative, I'll close the request.

I've definitely run into this myself previously as well.

The error suggests RSpec is looking for the Clearance helper in the wrong place:
```
Failure/Error: sign_in_as(user)
  NoMethodError:
    undefined method `sign_in_as' for #<RSpec::Core::ExampleGroup::Nested_1:0x007ffec67f1238>
```