Create assert_response_schema test helper

It is a common pattern to use JSON Schema to validate a API response[1], [2]
and [3].

This patch creates the `assert_response_schema` test helper that helps people do
this kind of validation easily on the controller tests.

[1]: https://robots.thoughtbot.com/validating-json-schemas-with-an-rspec-matcher
[2]: https://github.com/sharethrough/json-schema-rspec
[3]: rails-api#1011 (comment)

CHANGELOG.md

@@ -28,6 +28,7 @@ Features:
     CollectionSerializer for clarity, add ActiveModelSerializers.config.collection_serializer (@bf4)
 - [#1295](https://github.com/rails-api/active_model_serializers/pull/1295) Add config `serializer_lookup_enabled` that,
   when disabled, requires serializers to explicitly specified. (@trek)
+- [#1270](https://github.com/rails-api/active_model_serializers/pull/1270) Adds `assert_response_schema` test helper (@maurogeorge)
 
 Fixes:
 - [#1239](https://github.com/rails-api/active_model_serializers/pull/1239) Fix duplicates in JSON API compound documents (@beauby)

active_model_serializers.gemspec

@@ -46,6 +46,8 @@ Gem::Specification.new do |spec|
     # activesupport
     # activemodel
 
+  spec.add_runtime_dependency 'json-schema'
+
   # Soft dependency for pagination
   spec.add_development_dependency 'kaminari', ' ~> 0.16.3'
   spec.add_development_dependency 'will_paginate', '~> 3.0', '>= 3.0.7'

docs/README.md

@@ -22,6 +22,7 @@ This is the documentation of ActiveModelSerializers, it's focused on the **0.10.
 - [How to add root key](howto/add_root_key.md)
 - [How to add pagination links](howto/add_pagination_links.md)
 - [Using ActiveModelSerializers Outside Of Controllers](howto/outside_controller_use.md)
+- [Testing ActiveModelSerializers](howto/test.md)
 
 ## Integrations
 

docs/howto/test.md

@@ -0,0 +1,78 @@
+# How to test
+
+## Test helpers
+
+AMS provides a `assert_response_schema` method to be used on your controller tests to
+assert the response against a [JSON Schema](http://json-schema.org/). Let's take
+a look in a example.
+
+```ruby
+class PostsController < ApplicationController
+  def show
+    @post = Post.find(params[:id])
+
+    render json: @post
+  end
+end
+```
+
+To test the `posts#show` response of this controller we need to create a file in
+`test/support/schemas/posts/show.json` the helper uses a convention to the name
+of the file.
+
+This file is a JSON Schema representation of our response.
+
+```json
+{
+  "properties": {
+    "title" : { "type" : "string" },
+    "content" : { "type" : "string" }
+  }
+}
+```
+
+With all in place we can go to our test and use the helper.
+
+```ruby
+class PostsControllerTest < ActionController::TestCase
+  test "should render right response" do
+    get :index
+    assert_response_schema
+  end
+end
+```
+
+### Load a custom schema
+
+If we need to use other schema, for example when we have a namespaced API that
+shows the same response, we can pass the path of the schema.
+
+```ruby
+module V1
+  class PostsController < ApplicationController
+    def show
+      @post = Post.find(params[:id])
+
+      render json: @post
+    end
+  end
+end
+```
+
+```ruby
+class V1::PostsControllerTest < ActionController::TestCase
+  test "should render right response" do
+    get :index
+    assert_response_schema('posts/show.json')
+  end
+end
+```
+### Change the schema path
+
+By default all schemas are created at `test/support/schemas` if we are using
+RSpec for example we can change this to `spec/support/schemas` defining the
+default schema path in a initializer.
+
+```ruby
+ActiveModel::Serializer.config.schema_path = `spec/support/schemas`
+```

lib/active_model/serializer/assertions.rb

@@ -0,0 +1,16 @@
+require 'json-schema'
+
+module ActiveModel
+  class Serializer
+    module Assertions
+      def assert_response_schema(schema_path = nil)
+        controller_path = response.request.filtered_parameters[:controller]
+        action = response.request.filtered_parameters[:action]
+        schema_directory = ActiveModel::Serializer.config.schema_path
+        schema_path ||= "#{controller_path}/#{action}.json"
+        schema_full_path = "#{schema_directory}/#{schema_path}"
+        JSON::Validator.validate!(schema_full_path, response.body, strict: true)
+      end
+    end
+  end
+end

lib/active_model/serializer/configuration.rb

@@ -21,6 +21,7 @@ def config.array_serializer
 
         config.adapter = :attributes
         config.jsonapi_resource_type = :plural
+        base.config.schema_path = 'test/support/schemas'
       end
     end
   end

lib/active_model_serializers.rb

@@ -51,6 +51,7 @@ def silence_warnings
 require 'active_model/serializer'
 require 'active_model/serializable_resource'
 require 'active_model/serializer/version'
+require 'active_model/serializer/assertions'
 
 require 'action_controller/serialization'
 ActiveSupport.on_load(:action_controller) do
@@ -59,6 +60,7 @@ def silence_warnings
   ActionDispatch::Reloader.to_prepare do
     ActiveModel::Serializer.serializers_cache.clear
   end
+  ActionController::TestCase.send(:include, ActiveModel::Serializer::Assertions)
 end
 
 require 'active_model/serializer/railtie'

test/assertions_test.rb

@@ -0,0 +1,46 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class AssertionsTest < ActionController::TestCase
+      class MyController < ActionController::Base
+        def index
+          render json: Profile.new(name: 'Name 1', description: 'Description 1', comments: 'Comments 1')
+        end
+
+        def show
+          index
+        end
+      end
+
+      tests MyController
+
+      def test_that_assert_with_a_valid_schema
+        get :index
+        assert_response_schema
+      end
+
+      def test_that_raises_a_json_schema_with_a_invalid_schema
+        get :show
+        assert_raises JSON::Schema::ValidationError do
+          assert_response_schema
+        end
+      end
+
+      def test_that_assert_with_a_custom_schema
+        get :show
+        assert_response_schema('custom/show.json')
+      end
+
+      def test_that_assert_with_a_custom_schema_directory
+        original_schema_path = ActiveModel::Serializer.config.schema_path
+        ActiveModel::Serializer.config.schema_path = 'test/support/custom_schemas'
+
+        get :index
+        assert_response_schema
+
+        ActiveModel::Serializer.config.schema_path = original_schema_path
+      end
+    end
+  end
+end

test/support/custom_schemas/active_model/serializer/assertions_test/my/index.json

@@ -0,0 +1,6 @@
+{
+  "properties": {
+    "name" : { "type" : "string" },
+    "description" : { "type" : "string" }
+  }
+}

test/support/schemas/active_model/serializer/assertions_test/my/index.json

@@ -0,0 +1,6 @@
+{
+  "properties": {
+    "name" : { "type" : "string" },
+    "description" : { "type" : "string" }
+  }
+}

test/support/schemas/active_model/serializer/assertions_test/my/show.json

@@ -0,0 +1,5 @@
+{
+  "properties": {
+    "name" : { "type" : "string" }
+  }
+}

test/support/schemas/custom/show.json

@@ -0,0 +1,6 @@
+{
+  "properties": {
+    "name" : { "type" : "string" },
+    "description" : { "type" : "string" }
+  }
+}