Introduction to RSpec and Testing in Ruby

RSpec is a testing framework for Ruby. It is the most popular testing framework for Ruby, and is used in conjunction with the Ruby on Rails framework. Let's take a look at how to get started with RSpec.

Basics of RSpec

Install the RSpec gem:

gem install rspec

• It's convention to put all your tests in a spec folder.

Writing Tests

Describe Blocks

• use describe to describe a method or class
  • describe tells Rspec what code you're testing
  • you'll see these messages when you run your tests
  • the actual test code goes inside the describe block between the do and end

# inside spec/example_spec.rb
describe 'some class' do
	# some code
end

It Method

• Similar to other testing frameworks, we can use it to describe a test
• it is a single test
• we can have multiple it blocks inside a describe block
• it accepts a String as an argument
  • the string should describe what the test is doing (e.g. "returns true when given a positive number")

require_relative 'boat'

describe Boat do
  it 'should create boats' do
    expect(Boat.new).to be_a Boat
  end
end

Running a test

Run your test with rspec:

 rspec example_spec.rb

You should see something like this in your terminal as a result:

.

Finished in 0.00144 seconds (files took 0.06003 seconds to load)
1 example, 0 failures

Expect Method

• expect is used to expect a result from a test
• it marks an assertion that we expect to be true

describe Boat do
  it 'should create boats' do
    expect(Boat.new).to be_a Boat
  end

  it 'should have a name' do
    expect(Boat.new.name).to eq 'Boaty McBoatface'
  end
end

to Method

• use the to method to complete the assertion (e.g. expect(Boat.new).to be_a Boat)
• after to we can use a matcher to check for a specific result

Matchers

• Matchers are used to check for specific results

Common matchers:

• eq - checks for equality
• be_a - checks for a specific class
• be_empty - checks for an empty array
• be_truthy - checks for a truthy value
• be_falsey - checks for a falsy value
• include - checks if an array includes a specific value

Test-Driven Development

Let's add some methods on our Boat class and write some tests for them.

We are going to write our tests first, then write the code to make the tests pass.

describe Boat do
  it 'should create boats' do
    expect(Boat.new).to be_a Boat
  end
  describe '#allowed_aboard?' do   # describe block inside a describe block
  end
end

It is valid to nest describe blocks inside other describe blocks. This is useful for grouping tests together.

Notice the # before allowed_aboard?. This is a convention to indicate that we are testing an instance method.

Let's finish the test for the allowed_aboard? method:

describe Boat do
  it 'should create boats' do
    expect(Boat.new).to be_a Boat
  end
  describe '#allowed_aboard?' do
    it 'returns true if inventory includes a life jacket' do
      a_boat = Boat.new
      allowed = a_boat.allowed_aboard?(['life jacket', 'sun glasses'])
      expect(allowed).to be true
    end
  end
end

• the allowed_aboard? method takes an array of inventory as an argument
• returns true if the inventory includes a life jacket.
• use the to matcher to check if the result is true

If we run this test we will get the following error:

rspec boat_spec.rb
.F

Failures:

  1) Boat#allowed_aboard? returns true if inventory includes a life jacket
     Failure/Error: allowed = a_boat.allowed_aboard?(['life jacket', 'sun glasses'])

     NoMethodError:
       undefined method `allowed_aboard?' for #<Boat:0x000000010298e420>

             allowed = a_boat.allowed_aboard?(['life jacket', 'sun glasses'])
                             ^^^^^^^^^^^^^^^^
     # ./boat_spec.rb:10:in `block (3 levels) in <top (required)>'

Finished in 0.00158 seconds (files took 0.06525 seconds to load)
2 examples, 1 failure

Failed examples:

rspec ./boat_spec.rb:8 # Boat#allowed_aboard? returns true if inventory includes a life jacket

This tells us:

• we have an undefined method called allowed_aboard? for the Boat class

Let's write the code to make this test pass:

class Boat
  def allowed_aboard?(inventory)
    inventory.include?('life jacket')
  end
end

We should also test out the false case:

describe Boat do
  it 'should create boats' do
    expect(Boat.new).to be_a Boat
  end
  describe '#allowed_aboard?' do
    it 'returns true if inventory includes a life jacket' do
      a_boat = Boat.new
      allowed = a_boat.allowed_aboard?(['life jacket', 'sun glasses'])
      expect(allowed).to be true
    end
    it 'returns false if inventory does not include a life jacket' do
      a_boat = Boat.new
      allowed = a_boat.allowed_aboard?(['sun glasses'])
      expect(allowed).to be false
    end
  end
end

Setting up a project for RSpec

group :development, :test do
  gem 'rspec-rails', '~> 5.1'
  gem 'net-smtp', require: false
  # ...
end

• Add the rspec-rails gem to your Gemfile
• Add the net-smtp gem to your Gemfile
• if you have a current /spec folder, remove it rm -rf spec