custom_matcher.rb

RSpec::Matchers.define :included_nested do |*expected|
  match do |actual|
    include_nested(actual, expected)
  end

  def include_nested(actual, expected)
    expected.inject(actual) do |acc, ex|
      return false unless RSpec::Matchers::BuiltIn::Include.new(ex).matches?(acc)
      acc[ex]
    end

    true
  end

  failure_message_for_should do |actual|
    "expected that #{actual} would include [#{expected.map(&:inspect).join('][')}]"
  end

  failure_message_for_should_not do |actual|
    "expected that #{actual} would not include [#{expected.map(&:inspect).join('][')}]"
  end

  description do
    "include [#{expected.map(&:inspect).join('][')}]"
  end
end

subject do
  {
    'goods_detail' => {
      'expedited_shipping_cost' => 1.2
    }
  }
end

# Pass
it { should included_nested('goods_detail', 'expedited_shipping_cost') }   

# Fail
# expected that {"goods_detail"=>{"expedited_shipping_cost"=>1.2}} would include ["goods_detail"]["expedited_shipping_costx"][:foo]
it { should included_nested('goods_detail', 'expedited_shipping_costx', :foo) }