Cucumber may complain about cucumber.yml being invalid when it is valid

Running Cucumber tests while your cucumber.yml is 100% valid may still produce the following error.

cucumber.yml was found, but could not be parsed. Please refer to cucumber's documentation on correct profile usage.

This may in fact be due to your rerun file (e.g. tmp/rerun.txt) being invalid. Delete it and try again.

CarrierWave: How to generate versions with different file extensions

We use CarrierWave in many of our projects to store and serve files of various formats - mostly images. A common use case of CarrierWave's DSL is to "process" the original file in order to create multiple "versions", for example different resolutions of the same image.

Now we could go one step further: What if we want to create versions that have a different file extension than the original file? For example, let's assume we'd like to create a ve...


Ruby: Referencing global variables with the built-in English library

With Ruby's build-in library English you can reference global variables with an english name. This makes you code easier to read and is also suggested by Rubocop's Style/GlobalVars cop.

Example before:

if 'foo' =~ /foo/
  puts $~[1] # => foo

Example after:

if 'foo' =~ /foo/
  puts $LAST_MATCH_INFO[1] # => foo

Require pitfall in Rails

The English library is not loaded by default in Rails. S...

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cucumber_factory 2.1.1 released

We released a new version of cucumber_factory, which stabilizes the use of transient record references within your steps.

2.1.1 - 2020-05-20

Compatible changes

  • Cucumber 2.1.0 introduced some regressions which are being addressed with this patch:
    • Fix the assignment of polymorphic associations.
    • Restore the support for inherited traits within nested factories.

2.1.0 - 2020-03-09

Compatible changes

  • Allow associations to be set for [transient attribut...

How to update a single gem conservatively

The problem

Calling bundle update GEMNAME will update a lot more gems than you think. E.g. when you do this:

bundle update cucumber-rails

... you might think this will only update cucumber-rails. But it actually updates cucumber-rails and all of its dependencies. This will explode in your face when one of these dependencies release a new version with breaking API changes. Which is all the time.

In the example above updating cucumber-rails will give you Capybara 2.0 (because capybara is a dependency of `cucumber-rail...


How to grep through the DOM using the Capybara API

When your Cucumber feature needs to browse the page HTML, and you are not sure how to express your query as a clever CSS or XPath expression, there is another way: You can use all and find to grep through the DOM and then perform your search in plain Ruby.

Here is an example for this technique:

Then /^I should see an image with the filename...
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Five years of "Today I Learned" from Josh Branchaud

The linked GitHub repository is a bit like our "dev" cards deck, but groomed from a single person (Josh Branchaud). It includes an extensive list of over 900 TILs on many topics that might be interesting for most of us. (e.g. Ruby, Rails, Git, Unix..)


Here is an excerpt of all the Ruby TILs that were new to me. I encourage you to take your time to skim over the original list as well!

How to use Simplecov to find untested code in a Rails project with RSpec and Cucumber

Simplecov is a code coverage tool. This helps you to find out which parts of your application are not tested.

Integrating this in a rails project with rspec, cucumber and parallel_tests is easy.

  1. Add it to your Gemfile and bundle

    group :test do
      gem 'simplecov', require: false
  2. Add a .simplecov file in your project root:

    SimpleCov.start 'rails' do
      # any custom configs like groups and filters can be here at a central place



Async control flow in JavaScript: Promises, Microtasks, async/await

Slides for Henning's talk on Sep 21st 2017.

Understanding sync vs. async control flow

Talking to synchronous (or "blocking") API

print('script start')
html = get('/foo')
print('script end')

Script outputs 'script start', (long delay), '<html>...</html>', 'script end'.

Talking to asynchronous (or "evented") API

print('script start')
get('foo', done: function(html) {
print('script end')

Script outputs 'script start', `'...

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Cucumber: Identifying slow steps that drag down your test speed

In most projects I know, Cucumber test suite speed is not an issue. Of course, running 350 features takes its time, but still each test for itself is reasonably fast. There is nothing you can do to fundamentally speed up such a test (of course, you should be using parallel_tests).

However, in projects that go beyond clicking around in a web GUI and checking results, there might be various measures to speed things up. Katapult tests for example could be sped up more than 4 times by re...


Cucumber's table diffing does not play nice with Spreewald's `patiently do`

Turns out, Cucumber::MultilineArgument::DataTable#diff! caches some stuff. Code of the following form will not work as intended:

Then('some table should look like') do |expected_table|
  patiently do
    actual_table = calculate_actual_table
    expected_table.diff!(actual_table) # not actually patient, will keep failing if it failed the first time

Instead, simply use


Video transcoding: Web and native playback overview (April 2020)


Embedding videos on a website is very easy, add a <video> tag to your source code and it just works. Most of the time.

The thing is: Both the operating system and Browser of your client must support the container and codecs of your video. To ensure playback on every device, you have to transcode your videos to one or more versions of which they are supported by every device out there.

In this card, I'll explore the available audio and video standards we have right now. The goal is to built a pipeline that transcodes unknown ...

How to write good code comments

Code comments allow for adding human readable text right next to the code: notes for other developers, and for your future self.

As always, with great power comes great responsibility. Code comments can go wrong in many ways: they may become outdated, silently move away from the code they're referring to, restate the obvious, or just clutter files.

Good Comments

Here are some simple rules to keep your comments helpful:

Avoid stating what some code does – prefer the Why

Some say, perfect code would not need a single comment. Th...

Capybara: How to find a hidden field by its label

To find an input with the type hidden, you need to specify the type hidden:

find_field('Some label', type: :hidden)

Otherwise you will see an exception :

find_field('Some label')
# => Capybara::ElementNotFound: Unable to find field "Some label" that is not disabled`.

Note: Usually you don't need to check the input of hidden fields in an integration test. But e.g. waiting for a datepicker library to write the expected value to this field before continuing the test, which prevents flaky tests, is a valid use case.

How to make a cucumber test work with multiple browser sessions

Imagine you want to write a cucumber test for a user-to-user chat. To do this, you need the test to work with several browser sessions, logged in as separate users, at the same time.

Luckily, Capybara makes this relatively easy:


Scenario: Alice and Bob can chat
  Given Alice, Bob, and a chat session
  When I am signed in as "Alice"
    And I go to the chat
    And I am signed in as "Bob" [session: bob]
    And I go to the chat [session: bob]
    And I send the message "Hello, this is Alice!"
  Then I should see "Hello, this ...

Handling duplicate links with Capybara and Cucumber

Sometimes, you might have duplicate links on a page. Trying to click those links will by default cause Capybara to raise an Ambiguous match error.

If you do not care about which of those links are clicked, you can disable this errors by adding the following meta step:

When(/^(.*) \[allow ambiguous\]$/)do |step_text|
  prior_match_strategy = Capybara.match
  Capybara.match = :first
  Capybara.exact = prior_match_strategy

Use it with

When I follow "a duplicate link" [allow ambiguous]
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Taking screenshots in Capybara

Capybara-screenshot can automatically save screenshots and the HTML for failed Capybara tests in Cucumber, RSpec or Minitest.

Requires Capybara-Webkit, Selenium or poltergeist for making screenshots. They're saved into $APPLICATION_ROOT/tmp/capybara

The attached files contain config for cucumber integration and a Then show me a screenshot step.

Including assets for prettier presentation

Make sure to add this to config/environments/test.rb

# Do not generate digests fo...

Capybara 'fill_in': Ambiguous match for different input names

When you have two inputs, where one contains the name of the other (eg. Name and Name with special treatment), Capybara's fill_in method will fail with the following message:

Ambiguous match, found 2 elements matching visible field "Name" that is not disabled (Capybara::Ambiguous)

You can force Capybara to match exactly what you are typing (which makes your tests better anyways) with match: :prefer_exact:

name = 'Name'
value = 'Bettertest Cucumberbatch'
fill_in(field, with: value, match: :prefer_exact)


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