How do I test fulltext fields using sunspot_matchers in rspec?

My search controller does this:

search = Sunspot.search(Item) do
  fulltext params[:q] do
    fields(:foo, :bar, :bletch)
  end
end

And in my rspec controller test I have the following:

get :show, :q => q

expect(Sunspot.session).to have_search_params(:fulltext, q, proc do
  fields(:foo, :bar, :bletch)
end)

Side note: when I tried using a block instead of a proc, the block was never executed:

have_search_params(:fulltext, q) do
  # This block was never executed
end

My support/sunspot.rb contains only the following:

Sunspot.session = SunspotMatchers::SunspotSessionSpy.new(Sunspot.session)

When I run the test, I get the following error:

  1) SearchController GET search when a user runs a search performs a fulltext search on the right fields
     Failure/Error: fields(:foo, :bar, :bletch)
     NoMethodError:
       undefined method `fields' for #<Sunspot::DSL::Search:0x007fa0f0da0168>
     # ./spec/controllers/search_controller_spec.rb:28:in `block (5 levels) in <top (required)>'
     # ./spec/controllers/search_controller_spec.rb:27:in `block (4 levels) in <top (required)>'

What's the right way to test that my controller is supplying the correct params when doing a fulltext search? Google yields no relevant results when querying this problem.