Playing with RSpec from IRB

In this quick and easy guide you'll learn how to make rspec work on irb. Learn how to load, test and use rspec matchers and expectations in this quick tutorial.

Jan 10, 2019 • 2 Minute Read

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Introduction

This is a quick guide showing you necessary steps you should take to make rspec work on irb.

Implementation

Lets start by loading rspec core and expectations.

          require 'rspec/core' # this is what really runs your tests
require 'rspec/expectations' # readable syntax for checking properties of your code
    

We then include the matchers modules.

          include RSpec::Matchers # rspec will NOT automatically include this for you if you are using irb
    

With this we can now test out our expectations:

          >> expect(1).to eq(1)
=> true
    

Whooohoo! You are good to go.. Not really, try this out.

          2.3.0 :003 > array_hashes = [{lol: nil}]
 => [{:lol=>nil}]
2.3.0 :005 > include RSpec::Matchers
 => Object
2.3.0 :006 > expect(array_hashes).to include(have_key(:lol))
    

You will encounter an error as shown below:

          TypeError: wrong argument type RSpec::Matchers::BuiltIn::Has (expected Module)
        from (irb):6:in `include'
        from (irb):6
        from /usr/local/rvm/rubies/ruby-2.3.0/bin/irb:11:in `<main>'
    

If you read closely into the error it expects a Module as an argument, this is because when using irb we are running in the main ruby object. This object has another method called include that has presidence over rspec's include method

To work around this, we can prepend RSpec::Matchers onto main's singleton class:

          $ irb
irb(main):001:0> require 'rspec/expectations'
=> true
irb(main):002:0> singleton_class.prepend RSpec::Matchers
=> #<Class:#<Object:0x007ff08a8d6620>>
irb(main):003:0> array_hashes = [{lol: nil}]
=> [{:lol=>nil}]
irb(main):004:0> expect(array_hashes).to include(have_key(:lol))
=> true
    

We encountered this problem while doing a mob session at AgileVentures and raised the issue on the rspec expectations github page where we got this hack.