added spec for has_one-through relationship

spec/lib/extensions/active_record_spec.rb

@@ -71,3 +71,85 @@ class Account < ActiveRecord::Base
     File.delete(@db_file) if File.exist?(@db_file)
   end
 end
+
+describe 'active record has_one through' do
+  # Setup DB
+  before(:all) do
+    @db_file = "test_two.db"
+
+    # Open a database
+    db = SQLite3::Database.new @db_file
+
+    # Create tables
+    db.execute_batch <<-SQL
+      create table forests (
+        id int primary key,
+        name varchar(30)
+      );
+
+      create table trees (
+        id int primary key,
+        forest_id int,
+        name varchar(30),
+
+        FOREIGN KEY (forest_id) REFERENCES forests(id)
+      );
+
+      create table fruits (
+        id int primary key,
+        tree_id int,
+        name varchar(30),
+
+        FOREIGN KEY (tree_id) REFERENCES trees(id)
+      );
+    SQL
+
+    # Insert records
+    db.execute_batch <<-SQL
+      insert into forests values (1, 'sherwood');
+      insert into trees values (2, 1,'pine');
+      insert into fruits values (3, 2, 'pine nut');
+
+      insert into fruits(id,name) values (4,'apple');
+    SQL
+  end
+
+  # Setup Active Record
+  before(:all) do
+    class Forest < ActiveRecord::Base
+      has_many :trees
+    end
+
+    class Tree < ActiveRecord::Base
+      belongs_to :forest
+    end
+
+    class Fruit < ActiveRecord::Base
+      belongs_to :tree
+      has_one :forest, through: :tree
+    end
+
+    ActiveRecord::Base.establish_connection(
+      :adapter => 'sqlite3',
+      :database  => @db_file
+    )
+  end
+
+  context 'revenue' do
+    it 'has an forest_id' do
+      expect(Fruit.find(3).respond_to?(:forest_id)).to be true
+      expect(Fruit.find(3).forest_id).to eq 1
+      expect(Fruit.find(3).forest.name).to eq "sherwood"
+    end
+
+    it 'has nil if tree id not available' do
+      expect(Fruit.find(4).respond_to?(:tree_id)).to be true
+      expect(Fruit.find(4).forest_id).to eq nil
+    end
+  end
+
+  # Clean up DB
+  after(:all) do
+    File.delete(@db_file) if File.exist?(@db_file)
+  end
+end