module Rspec::Mocks::ArgumentMatchers

pairs. If the hash includes other keys, it will still pass.
Passes if the argument is a hash that includes the specified key(s) or key/value
object.should_receive(:message).with(hash_including(:key, :key2 => val2))
object.should_receive(:message).with(hash_including(:key))
object.should_receive(:message).with(hash_including(:key => val))
:call-seq:

def hash_including(*args)
  HashIncludingMatcher.new(anythingize_lonely_keys(*args))
end