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Updated: Capybara: Execute asynchronous JavaScript

Added a new section introducing an alternative to using evaluate_async_script which seems to work in newer Capybara versions.

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Changes to positional and keyword args in Ruby 3.0

Ruby 3.0 introduced a breaking change in how it treats keyword arguments.

There is an excellent blog post on the official Ruby blog going into the details. You should probably read that, but here is a slightly abbreviated version:

What changed

If you call a method that accepts keyword arguments, either explicitly or via **args, you cannot call it with a hash. I.e.

def explicit_kwargs(x:, y:)
  # ...

def splat_kwar...
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Spreewald 4.1.0 released

New steps:

  • When ... inside the ... iframe

New steps only available for Capybara 3+:

  • When I switch to the ... iframe
  • When I switch back to the whole page

The I switch back to the whole page step does not work reliably with Capybara 2 and lead to StaleReferenceErrors, therefore we decided to not make these steps available for Capybara 2.

Small improvements:

  • Trying to match against unsupported email headers will raise an error. Supported headers are "To", "CC", "BCC", "From", "Reply-To", "Subject", "Attachments"
  • It's ...

RubyMine: How to restore the Back to last position shortcut on Ubuntu 20.04

I really love to use the shortcuts CTRL+Alt+ Arrow Left and CTRL+Alt+ Arrow Right to navigate through the code. It worked great on Ubuntu 18.04 and MATE but after migrating to my new notebook with GNOME and Ubuntu 20.04, I realized that the shortcuts didn't work anymore. Well, it worked via Navigate > Back and also showed the shortcut, but my fingers weren't able to do this...

I cried a lot. (Why God? WHY?)

Then I found this [thread on StackOverflow](https://stackoverflow.com/questions/47808160/intellij-idea-ctrlaltleft-short...

Ruby: How to convert hex color codes to rgb or rgba

When you have a hex color code, you can easily convert it into its RGB values using plain Ruby.

>> "#ff8000".match(/^#(..)(..)(..)$/).captures.map(&:hex)
=> [255, 128, 0]

You can use that to implement a simple "hex to CSS rgba value with given opacity" method:

def hex_color_to_rgba(hex, opacity)
  rgb = hex.match(/^#(..)(..)(..)$/).captures.map(&:hex)
  "rgba(#{rgb.join(", ")}, #{opacity})"
>> hex_color_to_rgba("#ff8000", 0.5)
=> "rgba(255, 128, 0, 0.5)"

If you need to support RGBA hex color codes,...

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Rails 4 introduced collection_check_boxes

Starting from Rails 4.0, you can use a special form options helper called #collection_check_boxes. It behaves similar to #collection_select, but instead of a single select field it renders a checkbox and a label for each item in the collection.

= form_for @post do |form|
  = form.collection_check_boxes :author_ids, Author.all, :id, :name_with_initial

How generated form params look like


Capybara will not find links without an href attribute

Capybara will fail to find <a> tags that are missing an href attribute. This will probably happen to you every now and then on JavaScript-heavy applications.

An example would be an AngularJS application where the following HTML actually works. [1]

<a ng-click="hello()">Hello</a>

Capybara will fail to find that link, even though looking it up via the DOM shows it:

>> find_link("Hello")
Capybara::ElementNotFound: Unable to find link "Hello"

>> find("a").text
=> "Hello"

To make find_link and click_link work...


Running external commands with Open3

There are various ways to run external commands from within Ruby, but the most powerful ones are Open3.capture3 and Open3.popen3. Since those can do almost everything you would possibly need in a clean way, I prefer to simply always use them.

Behind the scenes, Open3 actually just uses Ruby's spawn command, but gives you a much better API.


Basic usage is

require 'open3'

stdout_str, error_str, status = Open3.capture3('/some/binary', 'with', 'some', 'args')
if status.success?...
Linked content

Online tool to convert tables between different formats

https://tableconvert.com/ is an only tool to convert tables between different formats (e.g. json, markdown, csv).
It also has a button to transpose a table ("rotate" it by 90 degree).


The tool can be handy if you have tests with large markdown tables for testing contents of a flat json structure or csv.

Please note that you should not use it with sensitive data (like all online tools in general).

Capybara: Preventing headless Chrome from freezing your test suite

We prefer to run our end-to-end tests with headless Chrome. While it's a very stable solution overall, we sometimes see the headless Chrome process freeze (or the Capybara driver losing connection, we're not sure).

The effect is that your test suite suddenly stops progressing without an error. You will eventually see an error after a long timeout but until then it will seem that your suite is frozen. If you're also using [capybara-screenshot](https:/...


Capybara: Waiting for outstanding AJAX requests after a test

When ending a Selenium test Capybara resets the browser state by closing the tab, clearing cookies, localStorage, etc.

It may be a good idea to wait for all in-flight AJAX requests to finish before ending a scenario:

  • You may have client-side JavaScript that freaks out when the tab closure kills their pending requests. If that JavaScript opens an error alert or spams errors to the console, your test may fail after the last step.
  • With unlucky timing the server may receive an AJAX request as the browser tab closes, causing a connection ...

E-mail deliverability

When your application is open for public sign up and sends out transactional e-mails to a large number of users, e-mail deliverability becomes an issue.

E-mail providers work hard to eliminate spam and have put in place relatively tight checks what kinds of emails they will accept, and from whom. To that end we use tools like mail-tester.com to make our mails as acceptable as possible. Unfortunately, there will always be providers that reject our e-mails for some reason or other, sometimes outside of our control.

For exa...


Capybara: Preventing server errors from failing your test

When your Rails application server raises error, Capybara will fail your test when it clears the session after the last step. The effect is a test that passes all steps, but fails anyway.

Capybara's behavior will help you to detect and fix errors in your application code. However, sometimes your application will explode with an error outside your control. Two examples:

  • A JavaScript library references a source map in its build, but forgets to package the source map
  • CarrierWave cleans up an upload or cache file after the record was delet...

Capybara: Pretending to interact with the document

Browsers blocks abusable JavaScript API calls until the user has interacted with the document. Examples would be opening new tab or start playing video or audio.

E.g. if you attempt to call video.play() in a test, the call will reject with a message like this:

NotAllowedError: play() failed because the user didn't interact with the document first. https://goo.gl/xX8pDD


To pretend document interaction in a test you can create an element, click on it, and remove the element again. This unblocks the entire JavaSc...


Rails route namespacing (in different flavors)

TL;DR There are three dimensions you can control when scoping routes:

scope module: 'module', path: 'path', as: 'as' do
  resources :examples, only: :index

=> Path Helpers: as_examples_path and as_examples_url
=> URLs: /path/examples
=> Controller module: Module::ExamplesController and views location: app/views/module/examples/

Changing URLs only

When you want to namespace some paths but leave the corresponding controllers and url helpers unaffected, you can use the scope method like follows:

scope path...

How to discard ActiveRecord's association cache

You know that ActiveRecord caches associations so they are not loaded twice for the same object. You also know that you can reload an association to make Rails load its data from the database again.

# discards cache and reloads and returns user.posts right away
# => [...]

If you want to discard the cache but not query the database (only the next time the association is accessed), you can use reset:

# discards cache, but does not load anything yet
# SQL query hap...

How to search through logs on staging or production environments

We generally use multiple application servers (at least two) and you have to search on all of them if you don't know which one handled the request you are looking for.

Rails application logs usually live in /var/www/<project-environment-name>/shared/log.
Web server logs usually live in /var/www/<project-environment-name>/log.

Searching through single logs with grep / zgrep

You can use grep in this directory to only search the latest logs or zgrep to also search older (already zipped) logs. zgrep is used just like grep a...

RSpec: How to test the content of a flash message in a request spec

The ActionDispatch module of Rails gives you the helper method flash to access the flash messages in a response.

describe PostsController, type: :request do

  describe 'update' do

    it 'shows a success message on update' do
      post_record = create(:post)

      put "/posts/#{post_record.id}"

      # Same as @request.flash[:alert]
      expect(flash[:alert]).to eq('Post updated successfully.')


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