Capybara steps to match stuff within any selector

These steps are now part of Spreewald.

Since Capybara 0.4.1 a within scope will only look at the first element that matches. We find this behavior to be impractical, but it is by design.

In order to perform a test or action in all matching elements, do not use within but prefer the attached "inside any" Cucumber steps like these:

When I follow "Foo" inside any "table"
Then I should see "Bar" inside any "li"

Fixing flaky integration tests

This card shows basic techniques for fixing a flaky integration test suite that sometimes passes and sometimes fails. "Integration test" is a test script that remote-controls a web browser with tools like Selenium WebDriver.

Although the examples in this card use Cucumber and Selenium, the techniques are applicable to all languages and testing tools.

Why tests are flaky

Your tests probably look like this:

When I click on A
When I click on B
When I click on C
Then I should see effects of C

A test like this works fine most of t…


Be careful to use correct HTTP status codes for maintenance pages

When your public-facing application has a longer downtime for server maintenance or long migrations, it's nice to setup a maintenance page to inform your users.

When delivering the maintenance page, be very careful to send the correct HTTP status code. Sending the wrong status code might get you kicked out of Google, or undo years of SEO work.

Here are some ways to shoot yourself in the foot durign maintenance:

  • If all your routes send a "200 OK" with a HTML body "We're b…

How to fix broken font collisions in wkhtmltopdf

If you are using PDFKit / wkhtmltopdf, you might as well want to use custom fonts in your stylesheets. Usually this should not be a problem, but at times they include misleading Meta-information that leads to a strange error in the PDF.

The setup

  • The designer gave you two fonts named something like BrandonText-Regular and BrandonText-Bold. (With flawed Meta-information)
  • You have a HTML string to be rendered by PDFKit
  • For demonstration purposes, this strin…
Linked content

How to exploit websites that include user input in their CSS

The linked article shows how to exploit websites that include unsanitized user input in their CSS.

Although the article often mentions React and CSS-in-JS libraries, the methods are applicable to any web app that injects user input into style tags or properties.

Also, sanitizing user input for CSS injection is much harder than sanitizing HTML.

Linked content

A Theme Switcher

Hack to implement an inverted "night mode" theme with a few lines of CSS.

Colors in images are preserved.

Linked content

How to enable the Thinkpad microphone mute key on Ubuntu 16.04

While the hardware mute button of my Lenovo x230 worked on Ubuntu 14.04 out of the box, it does not on Ubuntu 16.04. It is fairly simple to fix, though.

There is an extensive answer on Ask Ubuntu, but only part of it was required for me. Here is the gist of it.

  1. Open a terminal

  2. Run acpi_listen and press the mute key. You should see something like this:

    button/f20 F20 00000080 00000000 K

    Press Ctrl+C to exit.

  3. Run amixer scontrols. You will see multiple lines, one of which sh…

Rails: render a template that accepts a block by using the layout option of render

Let's say you have a form that you render a few times but you would like to customize your submit section each time. You can achieve this by rendering your form partial as layout and passing in a block. Your template or partial then serves as the surrounding layout of the block that you pass in. You can then yield back the form to the block and access the form in your block.


= form_for record do |form|

In order to make your template record/_form.haml accept a block whe…

Linked content

JavaScript bookmarklet to click an element and copy its text contents

Here is some JavaScript code that allows you to click the screen and get the clicked element's text contents (or value, in case of inputs).

The approach is simple: we place an overlay so you don't really click the target element. When you click the overlay, we look up the element underneath it and show its text in a browser dialog. You can then copy it from there.

It will also highlight the clicked element.

Here is the one-liner URL that you can store as a bookmark. Place it in your bookmarks bar and click it to activate.



An auto-mapper for ARIA labels and BEM classes in Cucumber selectors

Spreewald comes with a selector_for helper that matches an English term like the user's profile into a CSS selector. This is useful for steps that refer to a particular section of the page, like the following:

Then I should see "Bruce" within the user's profile

If you're too lazy to manually translate English to a CSS selector by adding a line to features/env/selectors.rb, we already have an [auto-mapper to translate English into …

JavaScript: Polyfill native Promise API with jQuery Deferreds

You should prefer native promises to jQuery's Deferreds. Native promises are much faster than their jQuery equivalent.

Native promises are supported on all browsers except IE <=11, Android <= 4.4 and iOS <= 7.

If you need Promise support for these old browsers y…

Deleting stale Paperclip attachment styles from the server

Sometimes you add Paperclip image styles, sometimes you remove some. In order to only keep the files you actually need, you should remove stale Paperclip styles from your server.

This script has been used in production successfully. Use at your own risk.

# Config #######################################################################
delete_styles = [:gallery, :thumbnail, :whatever]
scope = YourModel # A scope on the class with #has_attached_file
attachment_name = :image # First argument of #has_attached_file
noop …


How to solve Selenium focus issues

Selenium cannot reliably control a browser when its window is not in focus, or when you accidentally interact with the browser frame. This will result in flickering tests, which are "randomly" red and green. In fact, this behavior is not random at all and completely depends on whether or not the browser window had focus at the time.

This card will give you a better understanding of Selenium focus issues, and what you can do to get your test suite stable again.

Preventing accidental interaction with the Selenium window ——————–…

Linked content

Know what makes your browser pant

I figure we needed a definitive reference for what work is triggered by changing various CSS properties. It's something I get asked about often enough by developers, and while we can do tests with DevTools, I have both the time and inclination to shortcut that for everyone. I'm nice like that. —Paul Lewis

Selenium cannot obtain stable Firefox connection

When using geordi for integration tests you might get the following error when trying to run geordi cucumber:

unable to obtain stable firefox connection in 60 seconds ( (Selenium::WebDriver::Error::WebDriverError)

This means, that the vnc window the tests is talking to has no proper firefox version running. To figure out the issue this might help you:

  • Check if the .firefox-version (e.g. 24.0) is the same as ~/bin/firefoxes/24.0/firefox says in the browser
  • Maybe [rest…

Cancelling event propagation with jQuery

Within an event handler, there are no less than 4 methods to cancel event propagation, each with different semantics.

  • event.preventDefault()

    Only prevents the default browser behavior for the click, i.e. going to a different url or submitting a form.

  • event.stopPropagation()

    Only prevents the event from bubbling up the DOM. Note this effectively also cancels any event handlers attached through jQuery's live method, since those depend on bubbling.

  • event.stopImmediatePropagation()

    Prevents the event from bubbling up t…

How to make select2 use a Bootstrap 4 theme

select2 is a great jQuery library to make (large) <select> fields more usable.

For Bootstrap 3 there is select2-bootstrap-theme.
It won't work for Bootstrap 4, but rchavik's fork does (at least with Bootstrap 4 Alpha 6, current version at time of writing this).

It is based on a solution by angel-vladov and adds a few fixes.

Use it by addi…

Cucumber: Test that an element is not overshadowed by another element

I needed to make sure that an element is visible and not overshadowed by an element that has a higher z-index (like a modal overlay).

Here is the step I wanted:

Then the very important notice should not be overshadowed by another element

This is the step definition:

Then(/^(.*?) should not be overshadowed by another element$/) do |locator|
selector = selector_for(locator)
expect(page).to have_css(selector)
js = «-JS
var selector = #{selector.to_json};
var elementFromSelector = document.querySelector(selector)…

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