Cucumber pitfall: "Around" does not apply to your "Background" steps

Around will not happen until after a feature's Background has been processed. Use Before and After to avoid that.


Consider this Cucumber feature file:

Feature: Something that needs to be tested

    Given a user
      And I sign in        
  Scenario: Sign out
    When I sign out
    Then I should see "Signed out"
  Scenario: Something else
    # ...

Now, assume you have these step definitions:

Around do
  puts "** Around: before yield"    ...

Dealing with I18n::InvalidPluralizationData errors

When localizing model attributes via I18n you may run into errors like this:

I18n::InvalidPluralizationData: translation data { ... } can not be used with :count => 1. key 'one' is missing.

They seem to appear out of the blue and the error message is more confusing than helpful.

TL;DR A model (e.g. Post) is lacking an attribute (e.g. thread) translation.
Fix it by adding a translation for that model's attribute ( The error message reveals the (wrongly) located I18n data (from attributes.thread)….


Regex: Be careful when trying to match the start and/or end of a text

Ruby has two different ways to match the start and the end of a text:

  • ^ (Start of line) and $ (End of line)
  • \A (Start of string) and \z (End of string)

Most often you want to use \A and \z.

Here is a short example in which we want to validate the content type of a file attachment. Normally we would not expect content_type_1 to be a valid content type with the used regular expression image\/(jpeg|png). But as ^ and $ will match lines, it matches both content_type_1 and content_type_2. Using \A and \z will wo…

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Write custom RSpec matchers

There are three ways to define your own RSpec matchers, with increasing complexibility and options:

1) Use RSpec::Matchers.define

RSpec::Matchers.define :be_a_multiple_of do |expected|
  match do |actual|
    actual % expected == 0
  # optional
  failure_message do |actual|
    "expected that #{actual} would be a multiple of #{expected}"
  # optional
  failure_message_when_negated do |actual|
    "expected that #{actual} would not be a multiple of #{expected}"

This is automat…

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Gemika 0.4.0 released

We added support to read the include option from the travis.yml file. All combinations defined in the include option are added to the existing matrix. If no matrix exist, these are the only ones that are run.

This change should make it simpler to understand, which Ruby versions are actually run for a specific Gemfile.

Example with matrix

  - 2.1.8
  - 2.3.1
  - gemfiles/Gemfile1
  - gemfiles/Gemfile2

    - rvm: 2.6.3
      gemfile: gemfiles/Gemfile3

This will run all these 5 combinations: …


Ruby: How to use global variables for a conditional debugger

You can share a state in Ruby with global variables. Even if you should avoid them whenever possible, for debugging an application this could be temporary quite handy.


class User

  after_save { byebug if $debug; nil }

  def lock
   self.locked = true


Rspec.describe User do

let(:user) { create(:user) }

before do
# Many users are created and saved in this hook, but we don't want the debugger to stop for them
end …

DOM API for jQuery users

General hints on the DOM

  • the root of the DOM is document
  • custom elements inherit from HTMLElement. They need a - (dash) in their name, e.g. <notification-box>.
  • event listeners don't have event delegation à la .on('click', cssSelector, handler)


Action jQuery DOM API equivalent
Find descendant(s) by CSS selector .find(selector) one: `.querySelector(selecto…

CSS: Don't target multiple vendor-prefixed pseudo-elements in a single rule

Some pseudo-elements need to be addressed with vendor prefixes. E.g. ::selection is not supported by Firefox, you need to use ::-moz-selection instead.

What you cannot do is to define a single CSS rule to address both the standard and vendor-prefixed form:

::selection, ::-moz-selection {
  background-color: red;

This rule will be ignored by all browsers. The reason is that if a browser doe…

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CSS font metrics in detail

Line-height and vertical-align are simple CSS properties. So simple that most of us are convinced to fully understand how they work and how to use them. But it’s not. They really are complex, maybe the hardest ones, as they have a major role in the creation of one of the less-known feature of CSS: inline formatting context.

For example, line-height can be set as a length or a unitless value 1, but the default is normal. OK, but what normal is? We often read that it is (or should be) 1, or maybe 1.2, even the CSS spec is unclear on that…


Working with or without time zones in Rails applications

Rails supports time zones, but there are several pitfalls. Most importantly because and Time.current are completely different things and code from gems might use one or the other.

Especially configuring an application that cares only about one time zone is a bit tricky.

The following was tested on Rails 5.1 but should apply to Rails 4.2 as well.

Using only local time

Your life will be easier if your application does not need to support time zones. Disable them like this:

config.time_zone = 'Berlin' # Your local time…

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Updated: Git: Apply a diff

I tried to write a simpler example, when this might be handy.


RubyMine: Efficiently filtering results in the "Finder" overlay

RubyMine comes with a nice way to grep through your project's files: The finder (ctrl + shift + f). Don't be discouraged about the notice 100+ matches in n+ files if your searched keyword is too general or widely used in your project.


RubyMine comes with a few ways to narrow down the resulting list, don't hesitate to apply those filters to speed up your search. Your keybinding might vary based on your personal settings.

File mask (alt + k)

If you already know the file extension of your …

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Regular Expressions: Excessive backtracking can get yourself in trouble

Two weeks ago, Cloudflare was struck by a global outage that lasted ~30 minutes. The incident was rooted on a CPU exhaustion caused by a single regular expression containing some catastrophic backtracking:


This is a small reminder do keep using the lazy operator ? whenever possible and furthermore be aware that regular expressions should not only be unit-tested but also evaluated in terms of performance.


Beware of "nil" values in params

Recent rails security updates have shown that people make incorrect assumptions about the possible contents of the params hash.

Just don't make any! Treat it as what it is: potentially unsafe user input. For example:

/pages/edit?foo    --> params == {:foo => nil}
/pages/edit?foo[]  --> params == {:foo => [nil]} # at least in older rails 3 and in rails 2.x

Be especially wary about stuff like


If params[:password_reset_token] is nil, you'll retriev…


Webpack(er): A primer

webpack is a very powerful asset bundler written in node.js to bundle (ES6) JavaScript modules, stylesheets, images, and other assets for consumption in browsers.

Webpacker is a wrapper around webpack that handles integration with Rails.

This is a short introduction.


If you haven't already, you need to install node.js and Yarn.

Then, put

gem 'webpacker', '~> 4.x' # check if 4.x is still cu…

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Installing Ruby 2.3 or below on Ubuntu 17 and above

From Ubuntu 17, rbenv fails to install Ruby below 2.4 because of a mismatching OpenSSL dependency: it needs libssl1.0-dev for the installation process, but recent Ubuntus come with libssl-dev.

From the linked StackOverflow comment:

As far as I know (and tested), Ruby versions < 2.4 requires libssl1.0, while >2.4 libssl1.1+. The two libssl packages conflict with each other, so you can't have both of them, so I had to juggle the libs in order to install the required ruby version. To make things even funnier (or more complicated),…


Browsers will not send a referrer when linking from HTTPS to HTTP

  • When your site is on HTTPS and you are linking or redirecting to a HTTP site, the browser will not send a referrer.
  • This means the target site will see your traffic as "direct traffic", i.e. they cannot distinguish such hits from a user who directly typed in the URL.

Reasons for this behavior

It's probably because of this RFC:

Clients SHOULD NOT include a Referer header field in a (non-secure) HTTP request if the referring page was transferr…

Git: Apply a diff

git apply allows you to apply a diff onto your HEAD. Most often you can achieve the same result with a rebase & merge.


master                commit1 - commit3
feature-branch                \ commit2 - commit4
git checkout feature-branch
git reset --hard commit3
git diff ..commit4 | git apply
master                commit1 - commit3
feature-branch                          \ Unstaged commit 2 & 4

You can also [create a patch and apply it afterwards](…

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