```ruby
require 'test_helper'

class ProductTest < ActiveSupport::TestCase
  # test "the truth" do
  #   assert true
  # end
end
```

Add unit Test for product
user
```ruby
require 'test_helper'

class ProductTest < ActiveSupport::TestCase
  test "product attributes must not be empty" do
    product = Product.new
    assert product.invalid?
    assert product.errors[:title].any?
    assert product.errors[:description].any?
    assert product.errors[:image_url].any?
    assert product.errors[:price].any?
  end

  test "product price must be positive" do
    product = Product.new(:title => "Cookbook",
      :description => "Hello World",
      :image_url => "hello.jpg")

    product.price = -1

    assert product.invalid?
    assert_equal "must be greater than or equal to 0.01",
      product.errors[:price].join('; ')
    
    product.price = 0
    assert product.invalid?
    assert_equal "must be greater than or equal to 0.01",
      product.errors[:price].join('; ')

    product.price = 1
    assert product.valid?
  end
end
```
assistant