Ruby on rails RSpec：如何在两个不同的对象上期望有序消息？

如何在两个不同的对象上获得有序消息？目前我有这样的想法：

call_order = ''

expect(double1).to receive(:msg1) { call_order += '1' }
expect(double2).to receive(:msg2) { call_order += '2' }

expect(call_order).to eq '12'

我知道我可以使用以下方法在单个对象上获得有序消息：

expect(double).to receive(:msg).ordered
expect(double).to receive(:other_msg).ordered

根据rspec 3的规定，允许

collaborator_1 = double("Collaborator 1")
collaborator_2 = double("Collaborator 2")

expect(collaborator_1).to receive(:step_1).ordered
expect(collaborator_2).to receive(:step_2).ordered
expect(collaborator_1).to receive(:step_3).ordered

collaborator_1.step_1
collaborator_2.step_2
collaborator_1.step_3

#=> the examples should all pass