A Binary Search Implementation

bsearch.rb

class Bsearch

  def initialize(dictionary)
    @dictionary = Array(dictionary)
  end

  def search(value)
    search_in_chunk(@dictionary, value)
  end

  private

  def search_in_chunk(chunk, value)
    return (chunk[0] == value ? 0 : raise("Not Found")) if chunk.one?

    middle_index = middle_index(chunk)
    middle_value = chunk.at(middle_index)

    if middle_value == value
      return middle_index
    elsif middle_value > value
      return search_in_chunk(chunk[0...middle_index], value)
    elsif middle_value < value
      return (search_in_chunk(chunk[(middle_index)..-1], value) + middle_index)
    end
  end

  def middle_index(dict)
    dict.size / 2
  end
end

bsearch_test.rb

require 'minitest/autorun'
require_relative 'bsearch'

class TestBsearch < Minitest::Test
  def setup
    @bsearch = Bsearch.new([1,2,3,5,8,13])
  end

  def test_returns_value_in_array_to_right
    assert_equal 4, Bsearch.new([1,2,3,5,8,13]).search(8)
  end

  def test_returns_value_in_array_to_left
    assert_equal 0, Bsearch.new([1,2,3,5,8,13]).search(1)
  end

  def test_returns_raise_error_if_not_in_dictionary
    err = assert_raises(RuntimeError) { @bsearch.search(42) }
    assert_equal "Not Found", err.message
  end
end