diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 455412f..cb9eede 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -7,6 +7,7 @@
 require 'rspec'
 
 require File.expand_path '../../lib/yodatra.rb', __FILE__
+require File.expand_path '../../lib/yodatra/api_formatter.rb', __FILE__
 require File.expand_path '../../lib/yodatra/models_controller.rb', __FILE__
 require File.expand_path '../data/ar_models_controller.rb', __FILE__
 
@@ -15,6 +16,7 @@ module RSpecMixin
   def app
     Sinatra.new {
       use Yodatra::Base
+      use Yodatra::ApiFormatter
       use Yodatra::ModelsController
       use ArModelsController
     }
diff --git a/spec/unit/api_formatter_spec.rb b/spec/unit/api_formatter_spec.rb
new file mode 100644
index 0000000..858adf1
--- /dev/null
+++ b/spec/unit/api_formatter_spec.rb
@@ -0,0 +1,33 @@
+require File.expand_path '../../spec_helper.rb', __FILE__
+
+describe Yodatra::ApiFormatter do
+  let(:app) { proc{[200,{},['Hello, world.']]} }
+
+  before do
+    @stack = Yodatra::ApiFormatter.new(app, &bloc)
+    @request = Rack::MockRequest.new(@stack)
+  end
+
+  context 'with a unity bloc' do
+    let(:bloc) { proc{ |s,h,r| [s,h,r] } }
+
+    it 'transforms the response with the given block' do
+      response = @request.get('/')
+      expect(response.body).to eq 'Hello, world.'
+    end
+  end
+
+  context 'with an object wrapper bloc' do
+    let(:bloc) do
+      proc do |s,h,r|
+        transformed = r.map{ |rr| {data: rr}.to_json }
+        [s,h,transformed]
+      end
+    end
+
+    it 'transforms the response with the given block' do
+      response = @request.get('/')
+      expect(JSON.parse(response.body)['data']).to eq 'Hello, world.'
+    end
+  end
+end