def generate_expected_value
      if expected_difference.is_a? Range
        (before_value + expected_difference.first)..(before_value + expected_difference.end)
      else
        before_value + expected_difference
      end
    end
def generate_expected_value
      if expected_difference.is_a? Range
        (before_value + expected_difference.first)..(before_value + expected_difference.end)
      else
        before_value + expected_difference
      end
    end
Generate the expected value.

 @return [Integer, Range] Generate the expected value.