What about 

```ruby
shared_examples_for "Ohai::DSL::Plugin" do |ohai, plugin|
  describe "..." do
    ohai.should_receive ...
    plugin[:data].should ....
  end
end

...

describe "a plugin" do
  ohai = Ohai::System.new
  ohai.stub(:for_this_particular_test)
  plugin.stub(:for_this_particular_test)
  it_should_behave_like "Ohai::DSL::Plugin" ohai, plugin
end
```