Adding in spec file for has n :through

spec/dm_redis_associations_spec.rb

@@ -0,0 +1,54 @@
+require File.expand_path("../spec_helper", __FILE__)
+require 'dm-core'
+require 'dm-redis-adapter/spec/setup'
+
+describe DataMapper::Adapters::RedisAdapter do
+  before(:all) do
+    @adapter = DataMapper.setup(:default, {
+      :adapter  => "redis",
+      :db => 15
+    })
+  end
+
+  it "should allow has n :through" do
+    class Book
+      include DataMapper::Resource
+
+      property :id,   Serial
+      property :name, String
+
+      has n, :book_tags
+      has n, :tags, :through => :book_tags
+    end
+
+    class Tag
+      include DataMapper::Resource
+
+      property :id,   Serial
+      property :name, String
+
+      has n, :book_tags
+      has n, :books, :through => :book_tags
+    end
+
+    class BookTag
+      include DataMapper::Resource
+
+      property :id,   Serial
+      # property :book_id, Integer, :index => true
+      # property :tag_id,  Integer, :index => true
+
+      belongs_to :book
+      belongs_to :tag
+    end
+
+    b = Book.create(:name => "Harry Potter")
+    t = Tag.create(:name => "fiction")
+
+    b.tags << t
+    b.save
+
+    b2 = Book.get(1)
+    b2.tags.should == [t]
+  end
+end