How to mock message chaining with RSpec?

The cleanest way to test that code is to extract a method, e.g.

class Model < ActiveRecord::Base
  def self.some_scope_fields
    some_scope.pluck(:a_field)
  end
end

That method can be stubbed without a chain.

However, there are times when it's neither convenient nor idiomatic to do that. For example, it's idiomatic, and not a Law of Demeter violation, to call create on an ActiveRecord model's association methods. In those cases,

• if you don't care about method arguments, use receive_message_chain. stub_chain is deprecated; receive_message_chain is not. What the receive_message_chain documentation says is that "support for stub_chain parity may be removed in future versions". The issue linked to from that documentation makes it clear that "stub chain parity" means the use of with with receive_message_chain. So do use receive_message_chain; just don't use with with it.

• if you do care about method arguments, use doubles. For example, for the code you gave,

  scope = double
  allow(scope).to receive(:pluck).with(:a_field) { # return whatever }
  allow(Model).to receive(:some_scope).with(no_args) { scope }