Add tests for set_id method

Author: Shuhei Kitagawa

spec/lib/object_serializer_set_id_spec.rb

@@ -0,0 +1,30 @@
+require 'spec_helper'
+
+describe FastJsonapi::ObjectSerializer do
+  include_context 'movie class'
+
+  context 'when setting id' do
+    subject(:serializable_hash) { MovieSerializer.new(resource).serializable_hash }
+
+    before(:all) do
+      MovieSerializer.set_id :owner_id
+    end
+
+    context 'when one record is given' do
+      let(:resource) { movie }
+
+      it 'returns correct hash which id equals owner_id' do
+        expect(serializable_hash[:data][:id].to_i).to eq movie.owner_id
+      end
+    end
+
+    context 'when an array of records is given' do
+      let(:resource) { [movie, movie] }
+
+      it 'returns correct hash which id equals owner_id' do
+        expect(serializable_hash[:data][0][:id].to_i).to eq movie.owner_id
+        expect(serializable_hash[:data][1][:id].to_i).to eq movie.owner_id
+      end
+    end
+  end
+end