Everytime my Sidekiq process started, I was met with these errors:

WARN: DEPRECATION WARNING: Initialization autoloaded the constants ConfirmedUserGuard, ApplicationHelper, EmailHelper, ApplicationController, and OauthController.
Being able to do this is deprecated. Autoloading during initialization is going
to be an error condition in future versions of Rails.
Reloading does not reboot the application, and therefore code executed during
initialization does not run again. So, if you reload ConfirmedUserGuard, for example,
the expected changes won't be reflected in that stale Class object.
These autoloaded constants have been unloaded.
In order to autoload safely at boot time, please wrap your code in a reloader
callback this way:
    Rails.application.reloader.to_prepare do
      # Autoload classes and modules needed at boot time here.
    end
That block runs when the application boots, and every time there is a reload.
For historical reasons, it may run twice, so it has to be idempotent.
Check the "Autoloading and Reloading Constants" guide to learn more about how
Rails autoloads and reloads.

A large blob of text with specific warnings for:

• ConfirmedUserGuard
• ApplicationHelper
• EmailHelper
• ApplicationController
• OauthController

Cuprite is a pure Ruby driver for Capybara and a replacement for Selenium.

When using the Capybara method attach_file in your system tests, you might run into

Ferrum::TimeoutError: Timed out waiting for response. It's possible that this happened because something took a very long time (for example a page load was slow). If so, setting the :timeout option to a higher value might help.
Ferrum::BrowserError: Internal error

Heroku are great at pushing for upgrading to latest version of their hosted addons, below I summarized the steps I had to take to upgrade.

Heroku CI (continuous integration) runs tests in an environment very similar to an Heroku application, the code is packaged into a slug and runs on a dyno.

With Heroku's Github Integration it can automatically run CI-builds for every commit, then report back to Github with a pass or fail status and a link. The test results can be parsed if they are reported in the TAP-format, but it still stays on Heroku and is not visible on Github.

There are two concepts which greatly affected how I work with Rails development during the last couple of years, specifically with dependency management and preparing for upgrading to the next Rails version.

The first one is Dependabot which opens pull-requests to update one dependency at a time. This way of working felt natural at once and allowed me to be on top of dependency updates instead of being scared of it 👻.

The second one is dual-booting my Rails applications using separate lock-files, I was introduced to this concept by fastruby.io and their blog post Getting Ready for Rails 6.0: How to Dual Boot.

Unfortunately the two do not work well together out of the box 💔.

Error:
Documents::UploadJobTest#test_#perform_creates_an_activity_for_document:
MiniMagick::Error: `convert /tmp/shrine20201009-22018-5itpj9.pdf[0] -auto-orient /tmp/image_processing20201009-22018-1uk39lv.png` failed with error:
convert-im6.q16: not authorized `/tmp/shrine20201009-22018-5itpj9.pdf' @ error/constitute.c/ReadImage/412.
convert-im6.q16: no images defined `/tmp/image_processing20201009-22018-1uk39lv.png' @ error/convert.c/ConvertImageCommand/3258.

    app/uploaders/document_uploader.rb:13:in `block in <class:DocumentUploader>'
    test/jobs/documents/documents_upload_job_test.rb:8:in `block in <class:UploadJobTest>'

In my Ruby on Rails application, this error is raised when using MiniMagick to convert a PDF into an image. MiniMagick uses ImageMagick which uses Ghostscript for anything related to postscript files - for example PDFs.

Due to a security vulnerability in Ghostscript < 9.24, ImageMagick changed the default policy to not allow conversions using Ghostscript. Even if Ghostscript has fixed the vulnerability, the ImageMagick policy has not been changed.

Originally posted on my DEV.to page.

When using Heroku CI for automatic testing, the default output is just pass or fail without any parsing of how many tests passed or what errors where found.

This can be improved if you output the results in the Test Anything Protocol-format (TAP-format) according to Heroku.

This format is not built into the test frameworks used in Ruby on Rails. Therefore I had to write my own test reporter.