fibonacci_aggregator.rb

require 'test/unit'
extend Test::Unit::Assertions

class FibonacciAggregator
  class << self
    def sum_of_even_numbers(limit: 4_000_000, debug_mode: false)
      sum_of_numbers(limit: limit, debug_mode: debug_mode) do |number|
        number % 2 == 0
      end
    end

    private

    #For extensibility with other conditions for summing
    def sum_of_numbers(limit:, debug_mode:, &block)
      sum, lower, higher = 0, 1, 2

      while lower <= limit
        sum += lower if block.call(lower)
        puts ["Fibonacci number:", lower, "Sum of even numbers:", sum].join("\t") if debug_mode
        lower, higher = higher, lower + higher
      end

      sum
    end
  end
end

#tests
assert_equal(FibonacciAggregator.sum_of_even_numbers(limit: 5), 2)
assert_equal(FibonacciAggregator.sum_of_even_numbers(limit: 10), 2 + 8)
assert_equal(FibonacciAggregator.sum_of_even_numbers(limit: 100), 2 + 8 + 34)