# File lib/rspec/mocks/method_double.rb, line 135
      def add_expectation(error_generator, expectation_ordering, expected_from, opts, &implementation)
        configure_method
        expectation = if existing_stub = stubs.first
                        existing_stub.build_child(expected_from, 1, opts, &implementation)
                      else
                        MessageExpectation.new(error_generator, expectation_ordering, expected_from, @method_name, 1, opts, &implementation)
                      end
        expectations << expectation
        expectation
      end