Besides having an assignment outside a `let`, `before` or `it`, I really feel like having code duplication testing this kind of thing. Any change in this list will force me to open and modify two files: spec and implementation. If I already have the list in the implementation, no one should decide to change without expecting to "something" break.

My way of testing this is doing something like this:
```ruby
it "does not permit blacklisted fields" do
  # Here you use an attribute with less change to be removed from the list
  expect(policy.permitted?(:admin)).not_to be_true
end
```