possible.rb

class Foo < SimpleDelegator
  def in(&block)
    instance_eval &block
  end

  def have_awesomeness
    matcher do |target|
      expect(target).to eq 3
    end
  end

  def matcher(&block)
    Matcher.new(&block)
  end

  class Matcher
    def initialize(&block)
      @block = block
    end

    def matches?(target)
      @block.call(target)
      true
    end
  end
end

describe 'asdf' do
  it 'asfd' do
    hi = "hi"
    with(:foo) do
      expect(3).to have_awesomeness
    end
  end

  def with(sym, &block)
    Foo.new(self).in(&block)
  end
end