How to RSpec a shared ActiveRecord module without associated database table?

Question

Using RSpec 2.6 / Rails 3.1 / Postgres:

I am writing a supporting module (in my lib/) that any AR model can include. I'd like to write spec for this module. It needs to be included by an AR::Base model, because it loads associations when included and relies on some AR methods, but i don't want to use my existing model when writing rspec for this module.

I would just like to create an arbitrary AR model, but obviously it would not have a table associated in the database and AR is dying. Here's kindda what I want to do:

class SomeRandomModel < ActiveRecord::Base
  include MyModule

  # simulate DB attributes that MyModule would be using
  attr_accessor :foo, :bar, :baz 
end

describe SomeRandomModel do
  it '#some_method_in_my_module' do
    srm = SomeRandomModel.new(:foo => 1)
    srm.some_method_in_my_module.should eq(something)
  end
end

Of course, i get some error in postgres about the relation not existing.

Thanks for your help!

p1100i · Accepted Answer · 2013-08-02 12:16:10Z

16

There is an alternative way to solve this problem using rpsecs shared_examples_for, I mention few tricks in the code snippet but for more info see this relishapp-rspec-guide.

With this you can test your module in any of the classes which include it. So you really are testing what you use in your application.

Let's see an example:

# Lets assume a Movable module
module Movable
  def self.movable_class?
    true
  end

  def has_feets?
    true
  end
end

# Include Movable into Person and Animal
class Person < ActiveRecord::Base
  include Movable
end

class Animal < ActiveRecord::Base
  include Movable
end

Now lets create spec for our module: movable_spec.rb

shared_examples_for Movable do
  context 'with an instance' do
    before(:each) do
      # described_class points on the class, if you need an instance of it: 
      @obj = described_class.new

      # or you can use a parameter see below Animal test
      @obj = obj if obj.present?
    end

    it 'should have feets' do
      @obj.has_feets?.should be_true
    end
  end

  context 'class methods' do
    it 'should be a movable class' do
      described_class.movable_class?.should be_true
    end
  end
end

# Now list every model in your app to test them properly

describe Person do
  it_behaves_like Movable
end

describe Animal do
  it_behaves_like Movable do
    let(:obj) { Animal.new({ :name => 'capybara' }) }
  end
end

edited Aug 2, 2013 at 12:16

answered Aug 2, 2013 at 12:10

p1100i

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1 Comment

Pierre-Louis Gottfrois Over a year ago

This answer should be the one accepted. It's the proper way to handle module's spec.

goggin13 · Accepted Answer · 2012-05-16 19:04:05Z

15

I am facing a similar problem, and after much googling I have settled on just setting up and tearing down tables in my RSpec tests. Here's the snippet I've been using:

describe "stuff you are testing do" do

  before :all do
    m = ActiveRecord::Migration.new
    m.verbose = false  
    m.create_table :random_class do |t| 
      t.string :field_1
      t.integer :field_2
    end
  end

  after :all do
    m = ActiveRecord::Migration.new
    m.verbose = false
    m.drop_table :random_class
  end

  class RandomClass < ActiveRecord::Base
    attr_accessible :field_1, :field_2
  end

  # Your regular RSpec before(:each) blocks and tests
  # ...

  # e.g.
  it "should be able to use RandomClass" do
    rc = RandomClass.create! :field_1 => "hello", :field_2 => 5
    rc.field_1.should == "hello"
    rc.field_2.should == 5
  end

end

I'm not enamored of this solution, but it works. Hope that's helpful for someone! Either that or inspires them to post the best way to accomplish this.

:)

answered May 16, 2012 at 19:04

goggin13

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4 Comments

janechii Over a year ago

Yea, i gave up and used existing model lol. But this is pretty good too! Let me see if there's any other responses. Otherwise, this is a good answer! Thanks!

Milan Köpke Over a year ago

This might work, but it is not a good solution. You should not have to Look at burninggrammas answer for a better solution using rspecs shared_examples or also stackoverflow.com/questions/16453266/…

notapatch Over a year ago

I'm dinging this a point - I admire that you got something going but this is an accepted answer with more points than the best, simpler and more stable, answer (as pointed out by others - burninggramma's shared_examples_for)

janechii Over a year ago

I agree that @burninggrammas's answer is better and i've been doing that without realizing it for some time :)

Moustafa Samir · Accepted Answer · 2016-03-30 05:27:47Z

2

You can overwite self.columns

class Tableless < ActiveRecord::Base
  def self.columns
    @columns ||= [];
  end
end

then you can create a new instance reguralry

let(:dummy_instance) { Tableless.new }
it { is_expected.to be_valid}

answered Mar 30, 2016 at 5:27

Moustafa Samir

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1 Comment

depquid Over a year ago

In Rails 5.0, use def self.load_schema!; @columns_hash = {}; end

xnzac · Accepted Answer · 2013-05-09 08:46:07Z

0

goggin13, thanks for your answer. It mostly worked for me except that I had to change the migration instance methods to class ones. i.e.:

From

 m = ActiveRecord::Migration.new
 m.verbose = false  
 m.create_table ...

To

 m = ActiveRecord::Migration
 m.verbose = false  
 m.create_table ...

answered May 9, 2013 at 8:46

xnzac

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1 Comment

notapatch Over a year ago

The shared answer is the best (but unaccepted) answer by a long way and users shouldn't be confused with the more complicated and less stable answer.

Dan Benamy · Accepted Answer · 2013-06-13 18:18:29Z

0

Here's a slight variation on goggin13's answer which fixes the migrations (as Zac noted) and fixes the table name:

describe "stuff you are testing do" do

  before :all do
    m = ActiveRecord::Migration
    m.verbose = false  
    m.create_table :random_classes do |t| 
      t.string :field_1
      t.integer :field_2
    end
  end

  after :all do
    m = ActiveRecord::Migration
    m.verbose = false
    m.drop_table :random_classes
  end

  class RandomClass < ActiveRecord::Base
    attr_accessible :field_1, :field_2
  end

  # Your regular RSpec before(:each) blocks and tests
  # ...

  # e.g.
  it "should be able to use RandomClass" do
    rc = RandomClass.create! :field_1 => "hello", :field_2 => 5
    rc.field_1.should == "hello"
    rc.field_2.should == 5
  end

end

answered Jun 13, 2013 at 18:18

Dan Benamy

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1 Comment

notapatch Over a year ago

Dinging it a point as it adds support to goggin13's answer when the correct answer is shared_examples_for

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