You can use any RSpec matcher to match arguments of method calls

RSpec lets you define the arguments with which you expect a method to be invoked:

Copysubject.should_receive(:say).with('hello')

Sometimes you don't care about the exact arguments. For such cases RSpec comes with argument constraints like anything or hash_including:

Copysubject.should_receive(:update_attributes).with(hash_including(:message => 'hi world'))

You can go even further and use any RSpec matcher to match arguments:

Copysubject.should_receive(:say).with(instance_of(String))