tree.rb

  class Tree
    attr_reader :children, :item

    def initialize(item)
      @item = item
      @children = []
    end

    def add(child_item)
      children << Tree.new(child_item)
    end

    def search(search_item, &criteria)
      if criteria
        return self if criteria.call(item, search_item)
      else
        return self if search_item == item
      end

      children.each do |child|
        if block_given?
          result = child.search(search_item, &criteria)
        else
          result = child.search(search_item)
        end
        return result if result
      end

      nil
    end
  end

tree_test.rb

require 'test_helper'

describe "tree search" do
  let(:item) { [:a, :b, :c] }
  let(:tree) { Tree.new(item) }

  it "searches on the current node" do
    tree.search(item).must_equal tree
  end

  it "can search by passing in a block" do
    tree.search([:a, :z, :z]).must_be_nil
    tree.search([:a, :z, :z]){ |item, search_item| item.first == search_item.first  }.must_equal tree
  end

  describe "with children" do
    before { tree.add([:x, :y, :z]) }
    let(:child) { tree.children.first }

    it "can search on children" do
      tree.search([:x, :y, :z]).must_equal child
    end

    it "can search by passing in a block" do
      tree.search([:x, :z, :z]).must_be_nil
      tree.search([:x, :z, :z]){ |item, search_item| item.first == search_item.first  }.must_equal child
    end

    it "finds nothing on a failed search" do
      tree.search([:nothing]).must_be_nil
    end
  end
end