# File lib/active_support/testing/core_ext/test/unit/assertions.rb, line 38
      def assert_difference(expressions, difference = 1, message = nil, &block)
        expression_evaluations = Array(expressions).map do |expression|
          [expression, lambda do
            eval(expression, block.__send__(:binding))
          end]
        end

        original_values = expression_evaluations.inject([]) { |memo, expression| memo << expression[1].call }
        yield
        expression_evaluations.each_with_index do |expression, i|
          full_message = ""
          full_message << "#{message}.\n" if message
          full_message << "<#{expression[0]}> was the expression that failed"
          assert_equal original_values[i] + difference, expression[1].call, full_message
        end
      end