HashKeysDumper

hash_keys_dumper.rb

class HashKeysDumper
  def self.dump(hash)
    hash.map do |k, v|
      if v.is_a? Hash
        keys = dump(v)
        keys.map { |k1| [k, k1].join('.') }
      else
        k.to_s
      end
    end.flatten
  end
end

hash_keys_dumper_spec.rb

require 'hash_keys_dumper'

describe HashKeysDumper do
  describe '.dump' do
    subject { described_class.dump(hash) }

    context 'leaf element' do
      let(:hash) { { key: 'value' } }
      it { should == ['key'] }
    end

    context '2-level hash' do
      let(:hash) { { level1: { level2: 'value' } } }
      it { should == ['level1.level2'] }
    end

    context '2-level hash with 2 branches' do
      let(:hash) { { level1: { level21: 'value1', level22: 'value2' } } }
      it { should == ['level1.level21', 'level1.level22'] }
    end

    context '3-level hash with 3 branches' do
      let(:hash) { { level1: { level21: 'val', level22: { level31: 'value1', level32: 'value2' } } } }
      it { should == ['level1.level21', 'level1.level22.level31', 'level1.level22.level32'] }
    end
  end
end