Cop Idea: Prefer using the `all` matcher instead of iterating over an array

[backus]

The all matcher is pretty cool. We can't infer a lot of use cases statically of course but I bet we could probably detect enough cases for it to be useful. For example, I've seen some specs like this

it 'validates users' do
  [user1, user2, user3].each { |user| expect(user).to be_valid }
end

this could be written as

it 'validates users' do
  expect([user1, user2, user3].to all(be_valid)
end

[Darhazer]

I think it should ignore negative expectations.

it 'validates users' do
  [user1, user2, user3].each { |user| expect(user).not_to include(1) }
end

doesn't look right:

it 'validates users' do
  expect([user1, user2, user3]).not_to all(include(1))
end

RSpec suggest defining negate matchers in such a case, but I don't think this is something the cop will be able to suggest