chromedriver-helper gem in Gemfile might break you selenium tests (of other projects)
Summary: Don't add chromedriver-helper to the Gemfile
- the executables might break your tests in projects where
chromedriver-helperis not in the Gemfile - developers with different chrome versions will have problems using the same
chromedriver-helperversion
Background
If you install the chromedriver-helper gem, but don't have it in you Gemfile, your selenium tests might fail with:
Selenium::WebDriver::Error::WebDriverError: unable to connect to chromedriver 127.0.0.1:9515
The reason is that chromedriver-helper ov...
How to install packages from newer Ubuntu releases
We're usually running Ubuntu LTS versions. Sometimes newer hardware requires packages from more recent Ubuntu releases that only come with 6 months of support. If there is really no other way, it's possible to install packages from later Ubuntu releases
Caution: Pay really close attention to what you're doing. Depending on the package, this process may require upgrading a lot of dependencies, possibly breaking the system! You really should not do this unless you've carefully calculated the impact on your system
Preparation
First,...
JavaScript: Testing the type of a value
Checking if a JavaScript value is of a given type can be very confusing:
- There are two operators
typeofandinstanceofwhich work very differently. - JavaScript has some primitive types, like string literals, that are not objects (as opposed to Ruby, where every value is an object).
- Some values are sometimes a primitive value (e.g.
"foo") and sometimes an object (new String("foo")) and each form requires different checks - There are three different types for
null(null,undefinedandNaN) and each has different rules for...
Fixing flaky E2E tests
An end-to-end test (E2E test) is a script that remote-controls a web browser with tools like Selenium WebDriver. This card shows basic techniques for fixing a flaky E2E test suite that sometimes passes and sometimes fails.
Although many examples in this card use Ruby, 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
And I click on B
And I click on C
Then I should see effects of C
A test like this works fine...
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.
Popular footguns
Here are some ways to shoot yourself in the foot during maintenance:
- If all your routes send a "200 OK" with a HTML body "We're b...
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(html)
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(html)
})
print('script end')
Script outputs 'script start', 'script end', (long ...
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-RegularandBrandonText-Bold. (With flawed Meta-information) - You have a HTML string to be rendered by PDFKit
- For demonstration purposes, this strin...
How to add a custom dictionary to Ruby Mine
- Download the dictionary from http://www.winedt.org/dict.html, e.g.
http://www.winedt.org/dict/de_neu.zip unzip de_neu.zipmkdir ~/Documents/diciconv -f UTF-16 -t UTF-8 de_neu.dic -o ~/Documents/dic/de_neu_utf8.dic- In RubyMine: Go to Settings (CTRL + ALT + S) > Editor > Spelling > Dictionaries and add the folder
~/Documents/dic
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.
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.
-# record/_form.haml
= form_for record do |form|
-# ...
.form-actions
yield(form)
In order to make your template record/_form.haml accept a...
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 (attributes.post.thread). The error message reveals the (wrongly) located I18n data (from `attributes.thread...
Rails: wrap_parameters for your API
Rails 5 (don't know about the others) comes with an initializer wrap_parameters.rb. Here you can tell rails to wrap parameters send to your controllers for specific formats into a root node which it guesses from the controller name.
ActiveSupport.on_load(:action_controller) do
wrap_parameters format: [:json]
end
This would wrap a flat json body, like
{"name": "Konata"}
that gets send to your UsersController into
{"name" => "Konata", "user" => {"name" => "Konata"}}
Note that the params are now duplicat...
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 (127.0.0.1:7055) (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/firefoxsays in the browser - Maybe [rest...
How to make Webpacker compile once for parallel tests, and only if necessary
Webpack is the future. We're using it in our latest Rails applications.
For tests, we want to compile assets like for production.
For parallel tests, we want to avoid 8 workers compiling the same files at the same time.
When assets did not change, we do not want to spend time compiling them.
Here is our solution for all that.
Its concept should work for all test suites.
Copy the following to config/initializers/webpacker_compile_once.rb. It will patch Webpacker, but only for the test environment:
# Avoid hardcoded asset host...
Caution: Carrierwave has your file three times (temporarily)
When storing a file with Carrierwave, it is always cached prior to actually storing it (to support form roundtrips).
Carrierwave by default 1) copies the file to the cache and then 2) copies it again to its final destination (deleting the cached file immediately after storing). This means there are 3 (three) instances of a file on the disk at some point in time, and still 2 instances after Carrierwave is done if you do not remove...
How to: Rails cache for individual rspec tests
Rails default config uses the ActiveSupport::Cache::NullStore and disables controller caching for all environments except production:
config.action_controller.perform_caching = false
config.cache_store = :null_store
If you want to test caching you have at least two possibilities:
- Enable caching for every test (not covered by this card and straightforward)
- Enable caching for individual test
Enable caching for individual test (file cache)
1. Leave the defau...
Testing webpages globally (as in "around the globe")
These tools help you in checking websites globally:
- DNS Checker
-
This tool allows for global DNS propagation checking.
- GeoScreenshot
-
This tool takes screenshots of a given URL from various locations across the world.
How to define height of a div as percentage of its variable width
This is useful if, for example, you want to use a background-image that has to scale with the width and the div should only have the height of the picture.
html:
<div class="outer">
<div class="inner">
</div>
</div>
css:
.outer {
width: 100%;
background-image: image-url('background.png');
background-size: cover;
}
.inner {
padding-top: 60%;
}
How does it work?
There are several CSS attributes that can handle values as percentage. But they use different other attributes as "reference value...
Webmock normalizes arrays in urls
Typhoeus has a different way of representing array params in a get request than RestClient.
Typhoeus: http://example.com/?foo[0]=1&foo[1]=2&foo[2]=3
RestClient: http://example.com/?foo[]=1&foo[]=2&foo[]=3
Webmock normalizes this url when matching to your stubs, so it is always http://example.com/?foo[]=1&foo[]=2&foo[]=3. This might lead to green tests, but in fact crashes in real world. Rack::Utils.build_nested_query might help to build a get re...
Middleman: Use pretty URLs without doubling requests
By default Middleman generates files with a .html extension. Because of this all your URLs end in /foo.html instead of /foo, which looks a bit old school.
To get prettier URLs, Middleman lets you activate :directory_indexes in config.rb. This makes a directory for each of your pages and puts a single file index.html into it, e.g. /foo/index.html. This lets you access pages with http://domain/foo.
Don't double your requests!
Unfortunately you are now forcing every br...
Middleman configuration for Rails Developers
Middleman is a static page generator that brings many of the goodies that Rails developers are used to.
Out of the box, Middleman brings Haml, Sass, helpers etc. However, it can be configured to do even better. This card is a list of improvement hints for a Rails developer.
Gemfile
Remove tzinfo-data and wdm unless you're on Windows. Add these gems:
gem 'middleman-livereload'
gem 'middleman-sprockets' # Asset pipeline!
gem 'bootstrap-sass' # If you want to use Bootstrap
gem 'byebug'
gem 'capistrano'
gem 'capistrano-mid...
RSpec: Debug flickering test suites with rspec --bisect
In modern default RSpec configurations, your tests are usually run in random order. This helps to detect "flickering" tests that only fail when run in a certain order.
The reason for this are tests that have side effects causing other tests to fail later. The hard part is to find the offending test.
Enter rspec --bisect:
- Say you have a flickering test that passes on its own, but you just saw it fail in a full test run. At the top of the RSpec output, you will see a message like
Randomized with seed 12345. Take a note of the number....
Rubymine provides a visual merge conflict resolution tool
RubyMine provides a visual tool for resolving merge conflicts locally.
Follow
Git > Resolve Conflicts
in the context menu to open RubyMine's merge conflict tool.
- Left pane: local copy (read-only)
- Right pane: checked in version from repository (read-only)
- Central pane: base revision from which both conflicting versions are derived
You can also use a similar pane view to compare to files.
Mark two files and press Ctrl + D to compare.
How to use Parallel to speed up building the same html partial multiple times (for different data)
The parallel-gem is quite easy to use and can speed up rendering time if you want to render the same partial multiple times (e.g. for rendering long lists of things).
Parallel supports execution using forked processes (the default), threads (mind the GVL) and Ractors (some limitations for data sharing).
If your parallelized code talks to the database, you should [ensure not to leak database connections](https://makandracards.com/makandra/45360-using-activerecord-with-threads-will-leak-database-connect...