Getting started with rspec

Remarks#

RSpec is a BDD tool used to specify and test Ruby programs. It is used primarily to specify and test classes and methods, i.e. for unit testing.

The rspec gem is just a meta-gem which brings in the three parts of RSpec. Those three parts are also a way to structure this documentation.

rspec-core provides RSpec’s way of structuring and running tests: the rspec command-line executable, the describe, context and it methods, shared examples, etc. It is documented in the RSpec Core topic.
rspec-expectations provides RSpec’s support for expecting test results: the expect/to expectation syntax and RSpec’s built-in matchers. (It also provides the deprecated should expectation syntax.) It is documented in the RSpec Expectations topic.
rspec-mocks provides RSpec’s support for test doubles: double, allow, expect, receive, have_received, etc. It is documented in the RSpec Mocks topic.

There is also the rspec-rails gem, which extends RSpec with support for testing the types of classes used in Rails applications, and with support for writing feature specs (acceptance tests) which test the application from the user’s point of view.

Official documentation for RSpec and rspec-rails is here: https://www.relishapp.com/rspec

Installing RSpec

The most common way to install the RSpec gem is using Bundler. Add this line to your application’s Gemfile:

gem 'rspec'

And then execute bundle to install the dependencies:

$ bundle

Alternatively, you can install the gem manually:

$ gem install rspec

After installing the gem, run the following command:

rspec --init

This will create a spec folder for your tests, along with the following config files:

a spec directory into which to put spec files
a spec/spec_helper.rb file with default configuration options
an .rspec file with default command-line flags

A simple RSpec example

In greeter.rb (wherever that goes in your project):

class Greeter
  def greet
    "Hello, world!"
  end
end

In spec/greeter_spec.rb:

require_relative '../greeter.rb'

RSpec.describe Greeter do
  describe '#greet' do
    it "says hello" do
      expect(Greeter.new.greet).to eq("Hello, world!")
    end
  end
end

So our file structure looks like:

$ tree .
.
├── greeter.rb
└── spec
    └── greeter_spec.rb

1 directory, 2 files

Output

$rspec greeter_spec.rb
Finished in 0.00063 seconds (files took 0.06514 seconds to load)
1 example, 0 failures

In RSpec terminology, the file is a “spec” of Greeter and the it block is an “example”. The line with expect is an expectation. If the expectation is met, nothing happens and the test passes. If not, the test fails.

This example also shows that describe blocks can be nested, in this case to convey that the greet method is part of the Greet class. The # in #greet is only a convention to show that greet is an instance method (as opposed to ’.’ for a class method). RSpec doesn’t interpret the string at all, so you could use a different string or omit that describe block entirely.