Add spec to test when a published post is unpublished

spec/models/post_spec.rb

@@ -192,6 +192,16 @@
  post.save
  end
  end
+
+ describe 'a published post when' do
+ it 'has been changed to unpublished' do
+ post = FactoryBot.create(:post)
+ post.published_at = nil
+
+ expect(post).not_to receive(:notify_slack)
+ post.save
+ end
+ end
  end
 
  describe '#increment_likes' do