T159

Nested form
77行可以拔掉, 然後下面 78 & 80 可以一起測

````ruby
expect {
  put "/product_groups/#{product.product_group_id}", :product_group => update_product_data
}.to change(Product.count).by(1)
````

參考 : https://www.relishapp.com/rspec/rspec-expectations/v/2-0/docs/matchers/expect-change