Add tests for paged collections
user
```ruby
require 'test_helper'
require 'hal_api/paged_collection'
require 'test_models'
require 'kaminari'
require 'kaminari/models/array_extension'

describe HalApi::PagedCollection do

  let(:items)            { (0..25).collect{|t| TestObject.new("test #{t}", true) } }
  let(:paged_items)      { Kaminari::paginate_array(items).page(1).per(10) }
  let(:paged_collection) { HalApi::PagedCollection.new(paged_items, OpenStruct.new(params: {})) }

  it 'creates a paged collection' do
    paged_collection.wont_be_nil
    paged_collection.items.wont_be_nil
    paged_collection.request.wont_be_nil
  end

  it 'has delegated methods' do
    paged_collection.request.params.must_equal Hash.new
    paged_collection.params.must_equal Hash.new

    paged_collection.items.count.must_equal 10
    paged_collection.count.must_equal 10
    paged_collection.items.total_count.must_equal 26
    paged_collection.total.must_equal 26
  end

  it 'implements to_model' do
    paged_collection = HalApi::PagedCollection.new([])
    paged_collection.to_model.must_equal paged_collection
  end

  it 'is never persisted' do
    paged_collection = HalApi::PagedCollection.new([])
    paged_collection.wont_be :persisted?
  end

  it 'has a stubbed request by default' do
    paged_collection = HalApi::PagedCollection.new([])
    paged_collection.params.must_equal Hash.new
  end

  it 'will be a root resource be default' do
    paged_collection.is_root_resource.must_equal true
  end

  it 'will be a root resource based on options' do
    paged_collection.options[:is_root_resource] = false
    paged_collection.is_root_resource.must_equal false
  end

  it 'has an item_class' do
    paged_collection.item_class.must_equal(TestObject)
  end

  it 'has an item_decorator' do
    paged_collection.item_decorator.must_equal(Api::TestObjectRepresenter)
  end

  it 'has an url' do
    paged_collection.options[:url] = "test"
    paged_collection.url.must_equal "test"
  end

  it 'has a parent' do
    class TestFoo
      def self.columns
        @columns ||= [];
      end
    end

    class TestBar < TestFoo
      def becomes(klass); klass.new; end
      def self.base_class; TestFoo; end
    end

    a = TestBar.new
    a.wont_be_instance_of TestFoo
    paged_collection.options[:parent] = a
    paged_collection.parent.must_be_instance_of TestFoo
  end
end
```
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