Defining and calling lambdas or procs (Ruby)
Ruby has the class Proc
which encapsulates a "block of code". There are 2 "flavors" of Procs
:
- Those with "block semantics", called
blocks
or confusingly sometimes alsoprocs
- Those with "method semantics", called
lambdas
lambdas
They behave like Ruby method definitions:
- They are strict about their arguments.
-
return
means "exit thelambda
"
How to define a lambda
-
With the
lambda
keywordtest = lambda do |arg| puts arg end
-
With the lambda literal
->
(since Ruby 1.9.1)
...
Testing shared traits or modules without repeating yourself
When two classes implement the same behavior (methods, callbacks, etc.), you should extract that behavior into a trait or module. This card describes how to test that extracted behavior without repeating yourself.
Note that the examples below use Modularity traits to extract shared behavior. This is simply because we like to do it that way at makandra. The same techniques apply for modules and overriding self.included
.
Example
---...
Disable text-transforms in Selenium tests
Using text-transform: uppercase
- especially on form labels - can cause you serious headaches in Selenium tests. Sometimes the web driver will see the uppercase text, sometimes it won't, and umlauts will be a problem as well.
Simply disable it in tests, by
-
adding a body class for tests
%body{'data-environment' => Rails.env}
-
overriding the transforms
[data-environment="test"] * text-transform: none !important
How the Date Header Affects Cookie Expiration and Caching
tl;dr
When a cookie includes an
Expires
attribute or an HTTP response includes caching headers likeExpires
orCache-Control
, their validity depends on the server'sDate
header if present. Otherwise, the browser uses its local time. This can lead to issues in tests with mocked time or inconsistent cache behavior.
Cookie Expires
depends on the Date
header or browser time
When a cookie includes an Expires
attribute, the browser evaluates the expiration date relative to a reference time:
- If the HTTP response ...
Custom error messages in RSpec or Cucumber steps
Sometimes you have a test expectation but actually want a better error message in case of a failure. Here is how to do that.
Background
Consider this test:
expect(User.last).to be_present
In case of an error, it will fail with a not-so-helpful error message:
expected present? to return true, got false (Spec::Expectations::ExpectationNotMetError)
Solution
That can be fixed easily. RSpec expectations allow you to pass an error message like this:
expect(User.last).to be_present, 'Could not find a user!'
...
Test a download's filename with Cucumber
These steps are now part of Spreewald.
The step definitions below allow you to test the filename suggested by the server:
When I follow "Export as ZIP"
Then I should get a download with the filename "contacts_20110203.zip"
Capybara
Then /^I should get a download with the filename "([^\"]*)"$/ do |filename|
page.driver.response.headers['Content-Disposition'].should include("filename=\"#{filename}\"")
end
Webrat
Then /...
Rails: Testing file downloads with request specs
tl;dr
Prefer request specs over end-to-end tests (Capybara) to joyfully test file downloads!
Why?
Testing file downloads via Capybara is not easy and results in slow and fragile tests. We tried different approaches and the best one is just okay.
Tests for file downloads via Capybara ...
- ... are slow,
- ... are fragile (breaks CI, breaks if Selenium driver changes, ...),
- ... need workarounds for your specia...
Test your CSS rendering output with GreenOnion
No one wants to cry over regression issues in views; does testing HTML and CSS have to be such a back and forth between designers and devs? Why is it that the rest of the stack can have TDD and BDD but not the presentation layer? Well, GreenOnion is here to help you get the same results on testing front-end styling that you've enjoyed in your unit and integration tests up to now.
GreenOnion records 'skins', which are snapshots of the current state of a view (or any page that a browser can navigate to). The first time that it is run on a view...
RSpec: How to aggregate failures
RSpec >= 3.3 added aggregate_failures, which allows multiple failures in an example and list them all, rather than aborting on the first failure.
This can be used:
- In the global configuration
- With the tag
:aggregate_failures
(our preferred option in case every expectations should be aggregated) - With the method
aggregate_failures
[Here](https://web.archive.org/web/20210110131654/https://relishapp.com/rspec...
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.
Installation
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...
Automatically validating dependency licenses with License Finder
"Open-source software (OSS) is great. Anyone can use virtually any open-source code in their projects."
Well, it depends. Licenses can make things difficult, especially when you are developing closed-source software. Since some OSS licenses even require the employing application to be open-sourced as well (looking at you, GPL), you cannot use such software in a closed-source project.
To be sure on this, we have developed a project-level integration of Pivotal's excellent [license_finder](https:/...
Project management best practices: Technical debt summary
Maintaining larger projects makes it more difficult to balance refactoring and upgrade tasks according to its actual value. Consider to create and periodically maintain a summary, which helps you and your team in the decision which refactoring task should be taken next.
Template
Here is an template on how you might categorize your tasks:
| Technical debt | Estimated Efforts | Visible customer value| Customer value explained| Developer value|Developer value explained|
|-----------------------------|----------------|----------...
Heads up: Sidekiq per default silently fails when retries are exhausted!
For Sidekiq to be able to retry your jobs it has to be able to catch errors that occur while a job is executed.
Per default, Sidekiq will not raise / notify you if the retry count is exhausted. It will only copy the job to the dead queue (see wiki).
If you want to get notified, you have to implement it in your worker explicitly with a sidekiq_retries_exhausted
-block, e.g. like this:
class DownloadWorker
include Sidekiq::Worker
# Import jobs are retried a few time...
Guide to localizing a Rails application
Localizing a non-trivial application can be a huge undertaking. This card will give you an overview over the many components that are affected.
When you are asked to give an estimate for the effort involved, go through the list below and check which points are covered by your requirements. Work with a developer who has done a full-app localization before and assign an hour estimate to each of these points.
Static text
- Static strings and template text in
app
must be translated: Screens, mailer templates, PDF templates, helpe...
Ruby: How to use prepend for cleaner monkey patches
Let's say you have a gem which has the following module:
module SuperClient
def self.foo
'Foo'
end
def bar
'Bar'
end
end
For reasons you need to override foo
and bar
.
Keep in mind: Your code quality is getting worse with with each prepend
(other developers are not happy to find many library extensions). Try to avoid it if possible.
- Add a
lib/ext/super_client.rb
to your project (see How to organize monkey patches in Ruby on Rails projects) - Add the extension, which ov...
Ruby: A small summary of what return, break and next means for blocks
Summary
- Use
return
to return from a method.return
accepts a value that will be the return value of the method call. - Use
break
to quit from a block and from the method that yielded to the block.break
accepts a value that supplies the result of the expression it is “breaking” out of. - Use
next
to skip the rest of the current iteration.next
accepts an argument that will be the result of that block iteration.
The following method will serve as an example in the details below:
def example
puts yield
puts ...
Don't build randomness into your factories
Tests are about 100% control over UI interaction and your test scenario. Randomness makes writing tests hard. You will also push tests that are green for you today, but red for a colleague tomorrow.
That said, please don't do something like this:
Factory(:document) do |document|
document.category { ['foo', 'bar', 'baz'].sample }
end
Instead do this:
Factory(:document) do |document|
document.category 'foo'
end
The case against Faker
I even recommend to not use libraries like [Faker]...
How Haml 6 changes attribute rendering, and what to do about it
Haml 6 was a major rewrite with performance in mind. To achieve a performance improvement of 1.7x, some design trade-offs had to be made. The most notable change might be the simplified attribute rendering.
In Haml 5, attribute rendering knew two special cases: an attribute with value true
would be rendered without a value, an attribute with a falsy value would not be rendered at all. All other values would just be rendered as attribute values.
According to the Haml maintai...
Upgrading Rails 2 from 2.3.8 through 2.3.18 to Rails LTS
This card shows how to upgrade a Rails 2 application from Rails 2.3.8 through every single patch level up to 2.3.18, and then, hopefully, Rails LTS.
2.3.8 to 2.3.9
This release has many minor changes and fixes to prepare your application for Rails 3.
Step-by-step upgrade instructions:
- Upgrade
rails
gem - Change your
environment.rb
so it saysRAILS_GEM_VERSION = '2.3.9'
- Change your ...
Javascript: How to match text by Unicode properties
The linked MDN article is quite informative of a neat feature supported by all major browsers: Unicode character class escape.
You can use it to write regular expressions that work on the full UTF-8 space, not just Latin/ASCII. For example, a password policy matcher might include regular expressions like [A-z]
or [0-9]
, but those do not match e.g. German umlauts or [Eastern Arabic Numerals](https:/...
Capybara: Working with invisible elements
When Capybara locates elements in the DOM, by default it allows only accessing visible elements -- when you are using a driver that supports it (e.g. Selenium, not the default Rack::Test
driver).
Consider the following HTML:
<div class="test1">One<div>
<div class="test2">Two</div>
With some CSS:
.test1 { display: block }
.test2 { display: none }
We will be using Capybara's find
below, but this applies to any Capybara finder methods.
Default: visible: :visible
As described above, by default Capybara finds ...
How to not repeat yourself in Cucumber scenarios
It is good programming practice to Don't Repeat Yourself (or DRY). In Ruby on Rails we keep our code DRY by sharing behavior by using inheritance, modules, traits or partials.
When you reuse behavior you want to reuse tests as well. You are probably already reusing examples in unit tests. Unfortunately it is much harder to reuse code when writing integration tests with Cucumber, where you need to...
A different testing approach with Minitest and Fixtures
Slow test suites are a major pain point in projects, often due to RSpec
and FactoryBot
. Although minitest
and fixtures are sometimes viewed as outdated, they can greatly improve test speed.
We adopted a project using minitest and fixtures, and while it required some initial refactoring and establishing good practices, the faster test suite was well worth it! Stick with me to explore how these tools might actually be a good practice.
So, why is this setup faster? Partially, it's because minitest is more lightweight than RSpec
, which...
Accessing JavaScript objects from Capybara/Selenium
When testing JavaScript functionality in Selenium (E2E), you may need to access a class or function inside of a evaluate_script
block in one of your steps. Capybara may only access definitions that are attached to the browser (over the window
object that acts as the base). That means that once you are exporting your definition(s) in Webpacker, these won't be available in your tests (and neither in the dev console). The following principles/concepts also apply to Sprockets.
Say we have a StreetMap
class:
// street_map.js
class S...