Implicit using subject in rspec example doesn't work

问题

I'm going to test the model concern get_uniq_id method.

app/models/concerns/id_generation.rb

module IdGeneration
  extend ActiveSupport::Concern

  module ClassMethods
    def get_uniq_id
      id = ''
      loop {
        id = generate_id
        break unless Ticket.find_by_token(id)
      }
      id
    end

    def generate_id
      id = []
      "%s-%d-%s-%d-%s".split('-').each{|v| id << (v.eql?('%s') ? generate_characters : generate_digits)}
      id.join('-')
    end

    def generate_digits(quantity = 3)
      (0..9).to_a.shuffle[0, quantity].join
    end

    def generate_characters(quantity = 3)
      ('A'..'Z').to_a.shuffle[0, quantity].join
    end    
  end
end

spec/concerns/id_generation_spec.rb

require 'spec_helper'
describe IdGeneration do
  class Dummy
    include IdGeneration::ClassMethods
  end
  subject { Dummy.new }
  it { should get_uniq_id.match(/[A-Z]{2}-[0-9]{2}-[A-Z]{2}-[0-9]{2}-[A-Z]{2}/) }
end

It throws up the error:

 Failure/Error: it { should get_uniq_id.match(/[A-Z]{2}-[0-9]{2}-[A-Z]{2}-[0-9]{2}-[A-Z]{2}/) }
 NameError:
   undefined local variable or method `get_uniq_id' for #<RSpec::ExampleGroups::IdGeneration:0x00000001808c38>

If I specify the subject explicitly it { should subject.get_uniq_id.match(/[A-Z]{2}-[0-9]{2}-[A-Z]{2}-[0-9]{2}-[A-Z]{2}/) }. It works.

Do I need specify the subject explicitly?

回答1:

The way you're calling the method - yes. The method needs to be called on object. In this case, the get_uniq_id will be executed in context of currently running test, and this is why the error pops up.

The shortcut you can use might be like:

it { should respond_to :get_uniq_id }

Which will perform test similar to subject.respond_to?(:get_uniq_id). The method call however, needs explicit receiver.

You can update your test in order to use it as in your example, if you modify it slightly:

require 'spec_helper'
describe IdGeneration do
  class Dummy
    include IdGeneration::ClassMethods
  end
  subject { Dummy.new }

  def get_uniq_id
    subject.get_uniq_id
  end

  it { should get_uniq_id.match(/[A-Z]{2}-[0-9]{2}-[A-Z]{2}-[0-9]{2}-[A-Z]{2}/) }
end

Or, to bind the output to subject:

require 'spec_helper'
describe IdGeneration do
  class Dummy
    include IdGeneration::ClassMethods
  end

  let(:dummy) { Dummy.new }
  subject     { dummy }

  describe "#get_uniq_id" do
    subject { dummy.get_uniq_id }

    it { should match(/[A-Z]{2}-[0-9]{2}-[A-Z]{2}-[0-9]{2}-[A-Z]{2}/) }
  end
end

来源：https://stackoverflow.com/questions/29368762/implicit-using-subject-in-rspec-example-doesnt-work