RSpec - Subjects

One of RSpec’s strengths is that it provides many ways to write tests, clean tests. When your tests are short and uncluttered, it becomes easier to focus on the expected behavior and not on the details of how the tests are written. RSpec Subjects are yet another shortcut allowing you to write simple straightforward tests.

Consider this code −

class Person 
   attr_reader :first_name, :last_name 
   
   def initialize(first_name, last_name) 
      @first_name = first_name 
      @last_name = last_name 
   end 
end 

describe Person do 
   it 'create a new person with a first and last name' do
      person = Person.new 'John', 'Smith'
      
      expect(person).to have_attributes(first_name: 'John') 
      expect(person).to have_attributes(last_name: 'Smith') 
   end 
end

It’s actually pretty clear as is, but we could use RSpec’s subject feature to reduce the amount of code in the example. We do that by moving the person object instantiation into the describe line.

class Person 
   attr_reader :first_name, :last_name 
   
   def initialize(first_name, last_name) 
      @first_name = first_name 
      @last_name = last_name 
   end 
	
end 

describe Person.new 'John', 'Smith' do 
   it { is_expected.to have_attributes(first_name: 'John') } 
   it { is_expected.to have_attributes(last_name: 'Smith') }
end

When you run this code, you will see this output −

.. 
Finished in 0.003 seconds (files took 0.11201 seconds to load) 
2 examples, 0 failures

Note, how much simpler the second code sample is. We took the one it block in the first example and replaced it with two it blocks which end up requiring less code and are just as clear.