Rspec can't find route in controller test

I keep getting a routing error when testing a Rails 3.0 application with Rspec 3. It can't detect the route I'm using for my get request. Here's what my files look like:

routes.rb

resources :proficiency_tests do
  member do
    resource :lag_components, only: [:edit, :update]
  end
end

running rake:routes returns:

edit_lag_components GET    /proficiency_tests/:id/lag_components/edit(.:format)    {:action=>"edit", :controller=>"lag_components"}
     lag_components PUT    /proficiency_tests/:id/lag_components(.:format)         {:action=>"update", :controller=>"lag_components"}

controller is in:

app
|---controllers
    |---lag_components_controller.rb

Nothing special about the way the controller is set up.

spec is in:

spec
    |---controllers
        |---lag_components_controller.rb

tests are set up like this:

require 'spec_helper'

describe LagSubmissionsController do
  describe 'GET #edit' do
    let(:proficiency_test) { create :proficiency_test }

    it 'redirects' do
      *tests*    
    end
  end
end

Here is what I have tried and what the error messages have been:

get(:edit, id: proficiency_test.id)
# => No route matches {:id=>11259, :controller=>"lag_submissions", :action=>"edit"}

get(:edit, id: proficiency_test.id, use_route: :edit_lag_components)
# => No route matches {:id=>11260, :controller=>"lag_submissions", :action=>"edit"}

get("/proficiency_tests/#{proficiency_test.id}/lag_components/edit")
# => No route matches {:controller=>"lag_submissions", :action=>"/proficiency_tests/11258/lag_components/edit"}

The last one is particularly intriguing, because that is the exact route I use in the browser to render the edit page:

Does anyone know what's going on and why it can't find that route? Unfortunately, it's an older application and I can't change the routes around.