[RSpec] LEVEL 2 CONFIGURATION & MATCHERS

Installing RSpec

In this level we'll start by getting you setup on a regular Ruby project, then move onto using RSpec within Rails. Let's start by installing the rspec gem from the console.

gem install rspec

 

Command Line

With the RSpec gem installed, you will have access to the command line tool, rspec.

RSpec has a few settings you can configure, so to help us get started, let's initialize this as an RSpec project. This will generate a placeholder for our RSpec configuration.

rspec --init

 

Rails Configuration

Using rspec --init will setup RSpec within a ruby project, but for the rest of this course we'll be using RSpec within a Rails project. Run the rails generator to install RSpec into the current Rails project.

rails generate rspec:install

 

Running specs from the command line

We now have a Rails project all setup and we've created spec/models/zombie_spec.rb for you. Run this spec from the command line with color on, and specify documentation format.

rspec --color --format documentation spec/models/zombie_spec.rb

 

Predicate Matchers

Refactor the following spec to use an include matcher.

class Zombie < ActiveRecord::Base
  validates :name, presence: true
 
  def genius?
    iq >= 3
  end
end

Answer:

describe Zombie do
  it 'includes a tweet' do
    tweet = Tweet.new
    zombie = Zombie.new(tweets: [tweet])

    zombie.tweets.should include tweet

  end
end

 

Change Matcher

In the following example, we're checking to see that a method changes the state of a zombie. We need to make sure the zombie was in a specific state before and after the method is called.

Refactor the following example to use the expect and change syntax.

class Zombie < ActiveRecord::Base
  validates :name, presence: true
  validates :iq, numericality: true
 
  def eat_brains
    self.iq += 3
  end
end

Answer:

describe Zombie do
  it 'gains 3 IQ points by eating brains' do
    zombie = Zombie.new
    #zombie.iq.should == 0
    #zombie.eat_brains
    #zombie.iq.should == 3
    expect {zombie.eat_brains}.to change {zombie.iq}.from(0).to(3)
  end
end

#what expect {zombie.eat_brains}.to change {zombie.iq}.from(0).to(3)
#is saying that:
#zombie eat_brains
#then change zombie.iq
#from 0 to 3

# format:
#expect {action}.to change {value}.by(num) #or form(num1).to(num2)

Have Matcher

We're verifying the count to be greater than 0, but we really could be using a have matcher here to verify that the zombie has exactly one tweet. Refactor the spec to use the have matcher.

describe Zombie do
  it 'increases the number of tweets' do
    zombie = Zombie.new(name: 'Ash')
    zombie.tweets.new(message: "Arrrgggggggghhhhh")
    #zombie.tweets.count.should > 0
    zombie.should have(1).tweets
  end
end

Raises an Error

Testing for exceptions is tricky business. Refactor the spec below to use the raise_error matcher with an expect block.

class Tweet < ActiveRecord::Base
  attr_accessible :message
  belongs_to :zombie
  validates :message, presence: true
end

class Zombie < ActiveRecord::Base
  validates :name, presence: true
 
  class NotSmartEnoughError < StandardError; end
 
  def genius?
    iq >= 3
  end
 
  def make_decision!
    raise NotSmartEnoughError unless genius?
    return true
  end
end

Answer:

describe Zombie do
  it 'raises a Zombie::NotSmartEnoughError if not able to make a decision' do
    zombie = Zombie.new
    #begin
     # zombie.make_decision!
    # rescue Zombie::NotSmartEnoughError => e
      # e.should be_an_instance_of(Zombie::NotSmartEnoughError)
    # end
    expect {zombie.make_decision!}.to raise_error(
      Zombie::NotSmartEnoughError
      )
  end
end

 

More matchers: