rspec.rb

class Describe
  attr_reader :context_name

  def initialize(context_name, &block)
    @context_name = context_name
    instance_eval &block
  end

  def describe(context_name, &block)
    Describe.new(context_name, &block)
  end
end

## Helper method

def describe(context_name, &block)
  Describe.new(context_name, &block)
end

## Our test

describe NumberService do
  describe '#number' do

  end
end