Learning Rails: A Glossary

Posted on April 24, 2011 - Subscribe - Home

I've been teaching Rails to some people. One thing that's hard for them to get straight is the large number of tools involved in Rails development. This post is glossary of terms you may come across. Hopefully it will clarify things for you.

Acceptance Testing

Acceptancing testing is the act of testing use cases. Test cases are written in a way that describes a use case. Then a test case is passing it can be accepted. Cucumber is a good tool for acceptance testings. Work with your stake holder to develop tests that represent use cases. When the test is complete the feature should be accepted. Acceptance testing is focused around people outside the code development accepting features.

Application Servers - Thin, Mongrel, Passenger, Unicorn

These are all application servers. They interact with your Ruby code and respond to requests. They are integrated with web servers like Nginx or Apache to server you application on the internet.


Authentication is the process of matching credentials to a person and verifying them. Authentication is purely about identifiying who the user is--and not what they can do. Devise is an example of an authentication library.


Authorization is the process for determine what a specific user can do. Authorization usually involves permission or role based systems. CanCan is an example of an authorization library.

Behavior Driven Development (BDD)

Is essentially the same as TDD except using a different set of tools to express code in terms of user facing behavior. Rspec and Cucumber are part of the BDD toolbox.


Bundler reads a Gemfile and calculates a set of version requirements to make all the specified gems live happily together. It will prevent version conflicts and infamous 'gem already activated error'. It allows you to install git gems or standard gems from rubygems.org. It does not require libraries, it simply makes them available. It is up to you require them in your programs. Bundler can be used outside of rails. You should use bundler when you do any ruby work.


Capistrano is a tool for executing command one groups of remote (or local) serves over SSH. It is primary used to deploy Ruby (on Rails) application. It has support for multistage environments. Example, staging and production. You can easily write your own tasks similar to writing rake task. It is the preferred way deploy Rails applications.


Capybara is a gem designed to provide an abstraction layer between different browser drivers. It is primarily used in integration testing to interact with the web server. It provides an API to navigate between pages, click buttons, fill in forms, and other user interactions. It has adapters for many different browser drivers. Notable drivers include Selenium, rack-test and webrat.


Compass is a library built around SASS abstractions. It provides mixins for many common things like styling buttons and forms. It is also easy to extend and comes with many built in functions. The blueprint CSS framework is bundled by default.


Cucumber is a test framework for creating plain english acceptance tests. The tests can be executed automatically. Cucumber is used for integration testing web applications. The test suite is often used in CI (Continuous Integration). Cucumber uses a language called Gherkin to parse files into lines and match them against regular expressions. Regular expressions are matched with code blocks. Your test code lives in these blocks.

Cucumber tests are divided up into "Feature" files. Each feature has many "scenarios." Features are like use cases. Scenarios are different permutations of that use case. Here is an example Feature file:

Feature: Make Widthdrawls from Accounts
  As an account holder
  I want to use my money
  In order to use it buy thing

    Given I have account under "RubyX"
    And my account is activated

  Scenario: There is enough money in my account
    Given my account has "$1,000"
    And I'm at the bank
    When I widthdraw "$500"
    Then my account should have "$500"

  Scenario: There is not enough money in my account
    Given my account has "$1,000"
    And I'm at the bank
    When I widthdraw "$500"
    Then the teller should reject my transaction

Here is an example step definition:

Given /I'm at the bank/ do
  # set up pre conditions

Then /the teller should reject my transaction/ do
  # assert on things


DSL stands for Domain Specific Language. They are crafted to solve one or more problems very eloquently and nothing more. For example, a DSL created to declare work order would be horrible suited for writing Photoshop. DSLs are usually wrappers around more complicated methods that make it easier to express the intent of the underlying code from a programmer's perspective. You may have used a DSL before and not realized it. Here is an example from Sunspot's search functionality. It's designed for describing a search and nothing more:

Post.search do
  fulltext 'best pizza'
  with :blog_id, 1
  with(:published_at).less_than Time.now
  order_by :published_at, :desc
  paginate :page => 2, :per_page => 15
  facet :category_ids, :author_id


ERB is Embedded Ruby. ERB is built into the Ruby core. It allows to to place Ruby inside other files. For example, placing Ruby inside HTML. Here is an example:

<div class="<%= @ticket.state %>"
  <p><%= @ticket.message %></p>

Factories - FactoryGirl & Machinist

These are two popular libraries for creating object factories. They are usually used in test suites and population scripts. They provide a default set of attributes and allow programmers to specify the attributes they care about at creation time.


Git is a distributed version control system. Each user has a complete copy of the repository. Changes can be pushed back to the remote repositories for others to pull or push from. Linus Torvalds created Git because he was unsatisfied with other version control systems like CVS or SVN. Do not get GitHub confused with Git. GitHub is simply a service for hosting the main Git repository. You can use git independent of github, however most Ruby developers use github exclusively.


HAML is an HTML abstraction language. It's great for structuring documents and horrible to content. It will autoclose tags and lets you specify attributes as a hash. You can also include ruby code inside the templates. Here is an example:

  .content= simple_format(@post.content)


Ruby PaaS (Platform as a Service). They provide free cloud hosting for Rack applications with paid plans for increased resources. It is a very easy way to deploy your first application. Beware, they are easily owned by Amazon's AWS failure.


Metaprogramming is a term for dynamically generating code at runtime. Metaprogramming is why Rails feel the way it does. ActiveRecord associations to dynamically add methods to your classed based on how to declare them. Metaprogramming is possible in Ruby because it's a dynamic language interpreted at run time.

Open Classes & Monkey Patching

Ruby has open classes. This means you can simply declare methods insides a class that's already been defined. ActiveSupport uses open classes to add all those nice methods to core Ruby objects. This is how you can add a method to the String class:

class String
  def wtf?
    puts "wtf? " * self.length


Rake is like the Ruby version of make. You can create custom tasks that can be executed from the command line. rake db:migrate is a classic example. You can create as many tasks as you want. They can have prerequisites. They can also be in namespaces. A ':' designates tasks in different namespace. db:migrate means 'db' namespace, 'migrate' task. Multiple tasks can be executed in one go like so: rake db:create schema:load. They will be executed in the order they are listed. Rake was originally designed to be like make, but is often used to execute arbitrary code outside an application context. A cron job is a perfect example.

RJS (Ruby JavaScript)

RJS is an abomination. Don't use it. RJS uses ruby helpers to generate JavaScript to dump into HTML attributes violating UJS.


Rspec is a unit testing framework. It is based around the idea that test should describe behavior of classes in an english like way. Test files are called "specs". Spec files are divided into "examples." Examples contain matchers. Spec files can share examples. Here is an example spec file:

require 'spec_helper'

describe Post do
  it { should have_many(:comments) }

  describe "Post#out_dated?" do
    subject { Post.new :created_at => 2.months.ago }

    it { should be_outdated }


Rvm stands for Ruby Version Manager. It is a set of bash script designed to allow you switch out Ruby interpreters on the fly. It manages installed ruby interpreters and makes is very easy to install different implementations. It also manages Gemsets. Gemsets are groups of gemsets that are distinct from other groups (except the global gemset which shares gems between different ruby interpreters).


SASS and SCSS are CSS abstraction languages. They are compiled down to CSS. They allow you use variables, modules and include other files. In short, they make it much easier to write and main large amounts of CSS.


Selenium is a library that simulates user interaction with a browser. It runs the full browser. Selenium works best in FireFox, but can work in Chrome and other browsers. Commands are sent across as JavaScript which the browser evaluates to complete each action. Selenium is the most complete solution for simulating a user for your web application.

Test Driven Development (TDD)

The practice of writing a failing test first then completing the implementation. This makes the developer spend more time thinking about the code upfront while providing a solid test suite for the entire application. You can use Test::Unit for TDD in Ruby.


Test::Unit is a unit test framework built into Ruby 1.8. It is known as MiniTest in 1.9. It provides functionality for writing test cases with standard setup and tear down. Rails generates test files built in Test::Unit by default. It provides basic assertions. It's similar to jUnit or any member of the xUnit family. Here is an example:

require 'test_helper'

class PostTest < Test::Unit::TestCase 

  def test_out_dated? do
    post = Post.new :created_at => 2.months.ago

UJS (Unobstrusive JavaScript)

Unobtrusive JavaScript means separating JavaScript from the HTML. Specifying an onClick attribute in HTML is consider obtrusive because it obfuscates the markup. It is also hard to maintain because your javascript is harder to maintain. You can do the same thing unobtrusively by using jQuery to find the element by a class name and applying a click handler. Essentially UJS means keep JavaScript in .js files and HTML in .html files. Separation of church and state if you will.


Webrat is the original headless browser. It's similar to selenium, but much more implemented. It does not execute JavaScript and does not execute in a GUI. It is the most basic driver and is perfect for interacting with simple websites.

— Adam Hawkins