singleton?

lib/product.rb

@@ -0,0 +1,5 @@
+class Product
+  def initialize(type)
+    @type = type
+  end
+end

lib/products_controller.rb

@@ -0,0 +1,17 @@
+class ProductsController
+  # include Singleton - right way to do that
+
+  @instance = new
+
+  private_class_method :new
+
+  attr_accessor :product
+
+  def self.instance
+    @instance
+  end
+
+  def show
+    @product = PRODUCT
+  end
+end

spec/anything_spec.rb

@@ -8,11 +8,15 @@
 
 describe ProductsController do
   it 'cannot be instantiated via :new' do
+    expect{ ProductsController.new }.to raise_error NoMethodError
   end
 
   it 'can be instantiated only once' do
+    expect(ProductsController.instance.object_id).to eq(ProductsController.instance.object_id)
   end
 
   it 'does some work' do
+    ProductsController.instance.show
+    expect(ProductsController.instance.product).to be(PRODUCT)
   end
 end