```ruby
require 'test_helper'

class SiteTest < ActiveSupport::TestCase
  setup do
    @site = Site.create(name: "name",
                        js_url: "http://example.com/application.js",
                        css_url: "http://example.com/application.css")
    @post = @site.posts.create(title: "title", body: "body", original_id: 1)
    Tempfile.open do |file|
      @post.images.create(image: file)
    end
  end

  test 'destroy site' do
    assert_equal(1, Site.count)
    assert_equal(1, Post.count)
    assert_equal(1, Image.count)
    @site.destroy
    assert_equal(0, Site.count)
    assert_equal(0, Post.count)
    assert_equal(0, Image.count)
  end
end
```

Use `create!` instead of `create`
user
```ruby
require 'test_helper'

class SiteTest < ActiveSupport::TestCase
  setup do
    @site = Site.create!(name: "name",
                         js_url: "http://example.com/application.js",
                         css_url: "http://example.com/application.css")
    @post = @site.posts.create!(title: "title", body: "body", original_id: 1)
    Tempfile.open do |file|
      @post.images.create!(image: file)
    end
  end

  test 'destroy site' do
    assert_equal(1, Site.count)
    assert_equal(1, Post.count)
    assert_equal(1, Image.count)
    @site.destroy
    assert_equal(0, Site.count)
    assert_equal(0, Post.count)
    assert_equal(0, Image.count)
  end
end
```
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