How to test a scope in Rails 3

Question

What's the best way to test scopes in Rails 3. In rails 2, I would do something like:

Rspec:

it 'should have a top_level scope' do
  Category.top_level.proxy_options.should == {:conditions => {:parent_id => nil}}
end

This fails in rails 3 with a "undefined method `proxy_options' for []:ActiveRecord::Relation" error.

How are people testing that a scope is specified with the correct options? I see you could examine the arel object and might be able to make some expectations on that, but I'm not sure what the best way to do it would be.

Answer 1

Leaving the question of 'how-to-test' aside... here's how to achieve similar stuff in Rails3...

In Rails3 named scopes are different in that they just generate Arel relational operators. But, investigate!

If you go to your console and type:

# All the guts of arel!
Category.top_level.arel.inspect

You'll see internal parts of Arel. It's used to build up the relation, but can also be introspected for current state. You'll notice public methods like #where_clauses and such.

However, the scope itself has a lot of helpful introspection public methods that make it easier than directly accessing @arel:

# Basic stuff:
=> [:table, :primary_key, :to_sql]

# and these to check-out all parts of your relation:
=> [:includes_values, :eager_load_values, :preload_values,
    :select_values, :group_values, :order_values, :reorder_flag,
    :joins_values, :where_values, :having_values, :limit_value,
    :offset_value, :readonly_value, :create_with_value, :from_value]

# With 'where_values' you can see the whole tree of conditions:
Category.top_level.where_values.first.methods - Object.new.methods
=> [:operator, :operand1, :operand2, :left, :left=, 
    :right, :right=, :not, :or, :and, :to_sql, :each]

# You can see each condition to_sql
Category.top_level.where_values.map(&:to_sql)
=> ["`categories`.`parent_id` IS NULL"]

# More to the point, use #where_values_hash to see rails2-like :conditions hash:
Category.top_level.where_values_hash
=> {"parent_id"=>nil}

Use this last one: #where_values_hash to test scopes in a similar way to #proxy_options in Rails2....

Answer 2

Ideally your unit tests should treat models (classes) and instances thereof as black boxes. After all, it's not really the implementation you care about but the behavior of the interface.

So instead of testing that the scope is implemented in a particular way (i.e. with a particular set of conditions), try testing that it behaves correctly—that it returns instances it should and doesn't return instances it shouldn't.

describe Category do
  describe ".top_level" do
    it "should return root categories" do
      frameworks = Category.create(:name => "Frameworks")

      Category.top_level.should include(frameworks)
    end

    it "should not return child categories" do
      frameworks = Category.create(:name => "Frameworks")
      rails = Category.create(:name => "Ruby on Rails", :parent => frameworks)

      Category.top_level.should_not include(rails)
    end
  end
end

If you write your tests in this way, you'll be free to re-factor your implementations as you please without needing to modify your tests or, more importantly, without needing to worry about unknowingly breaking your application.

Answer 3

This is how i check them. Think of this scope :

  scope :item_type, lambda { |item_type|
    where("game_items.item_type = ?", item_type )
  } 

that gets all the game_items where item_type equals to a value(like 'Weapon') :

    it "should get a list of all possible game weapons if called like GameItem.item_type('Weapon'), with no arguments" do
        Factory(:game_item, :item_type => 'Weapon')
        Factory(:game_item, :item_type => 'Gloves')
        weapons = GameItem.item_type('Weapon')
        weapons.each { |weapon| weapon.item_type.should == 'Weapon' }
    end

I test that the weapons array holds only Weapon item_types and not something else like Gloves that are specified in the spec.