What does assign method do in testing ?

*assigns* - _Any objects that are stored as instance variables in actions for use in views._ (Testing Rails Applications — Ruby on Rails Guides)

I have a code :-

  test "should update line_item" do     patch :update, id:@line_item, line_item: { cart_id:@line_item.cart_id, product_id:@line_item.product_id}     assert_redirected_to line_item_path(assigns(:line_item))   end

Does *assigns(:line_item)* give back an instance of the model _LineItem_ ? I am bit confused with the use of the method *assigns*.