I find these spec_helpers really useful

I think it might be controversial, but I'm putting these in to start the conversation.  I've been using these to make my specs really dry.

```ruby
context 'searching for foos' do
  before do
    @foo_a = FactoryGirl.create :foo, bar: true
    @foo_b = FactoryGirl.create :foo, bar: false
  end
  it 'returns all results' do
    get '/foos'
    expect_count_of 2
  end
  it 'does not return foo which has something' do
    get '/foos', bar: true
    expect_to_have @foo_a
    expect_to_not_have @foo_b
  end
  it 'returns only the requested foo' do
    get "/foos/#{@foo_a.id}"
    expect_only @foo_a
  end
end
```