implement sparse fieldsets http://jsonapi.org/format/#fetching-sparse-fieldsets

test/adapter/json_api/fieldset_test.rb

@@ -0,0 +1,56 @@
+require 'test_helper'
+
+module ActiveModel
+  class Serializer
+    class Adapter
+      class JsonApi
+        class FieldsetTest < Minitest::Test
+          def setup
+            @post = Post.new(title: 'New Post', body: 'Body')
+            @first_comment = Comment.new(id: 1, body: 'ZOMG A COMMENT')
+            @second_comment = Comment.new(id: 2, body: 'ZOMG ANOTHER COMMENT')
+            @post.comments = [@first_comment, @second_comment]
+            @first_comment.post = @post
+            @second_comment.post = @post
+
+            @serializer = PostSerializer.new(@post)
+            @adapter = ActiveModel::Serializer::Adapter::JsonApi.new(@serializer)
+          end
+
+          def teardown
+            @serializer = nil
+            @adapter = nil
+          end
+
+          def test_fieldset_with_fields_array
+            fieldset = ActiveModel::Serializer::Fieldset.new(@serializer, ['title'])
+
+            assert_equal(
+              {:title=>"New Post", :links=>{:comments=>["1", "2"]}}, 
+              @adapter.serializable_hash({fieldset: fieldset})[:posts]
+            )
+          end
+
+          def test_fieldset_with_hash
+            fieldset = ActiveModel::Serializer::Fieldset.new(@serializer, {post: [:body]})
+
+            assert_equal(
+              {:body=>"Body", :links=>{:comments=>["1", "2"]}}, 
+              @adapter.serializable_hash({fieldset: fieldset})[:posts]
+            )
+          end
+
+          def test_fieldset_with_multiple_hashes
+            fieldset = ActiveModel::Serializer::Fieldset.new(@serializer, {post: [:title], comment: [:body]})
+
+            assert_equal(
+              [{:body=>"ZOMG A COMMENT" }, {:body=>"ZOMG ANOTHER COMMENT"}],
+              @adapter.serializable_hash({fieldset: fieldset})[:linked][:comments]
+            )
+          end
+
+        end
+      end
+    end
+  end
+end

test/serializers/attributes_test.rb

@@ -12,7 +12,11 @@ module ActiveModel
         assert_equal([:name, :description],
                      @profile_serializer.class._attributes)
       end
+
+      def test_attributes_with_fields_option
+        assert_equal({name: 'Name 1'},
+                     @profile_serializer.attributes( { fields: [:name] } ) )
+      end
     end
   end
 end
-