Add specs for pipeline serializer with pagination

app/serializers/pipeline_serializer.rb

 class PipelineSerializer < BaseSerializer
   entity PipelineEntity
+  class InvalidResourceError < StandardError; end
   include API::Helpers::Pagination
   Struct.new('Pagination', :request, :response)
 
   def represent(resource, opts = {})
-    if paginate?
+    if paginated?
+      raise InvalidResourceError unless resource.respond_to?(:page)
+
       super(paginate(resource), opts)
     else
       super(resource, opts)
     end
   end
 
-  def paginate?
+  def paginated?
     defined?(@pagination)
   end
 

spec/serializers/pipeline_serializer_spec.rb

@@ -2,17 +2,100 @@ require 'spec_helper'
 
 describe PipelineSerializer do
   let(:user) { create(:user) }
-  let(:pipeline) { create(:ci_empty_pipeline) }
 
   let(:serializer) do
     described_class.new(user: user)
   end
 
+  let(:entity) do
+    serializer.represent(resource)
+  end
+
+  subject { entity.as_json }
+
   describe '#represent' do
-    subject { serializer.represent(pipeline) }
+    context 'when used without pagination' do
+      it 'created a not paginated serializer' do
+        expect(serializer).not_to be_paginated
+      end
+
+      context 'when a single object is being serialized' do
+        let(:resource) { create(:ci_empty_pipeline) }
 
         it 'serializers the pipeline object' do
-      expect(subject.as_json).to include :id
+          expect(subject[:id]).to eq resource.id
+        end
+      end
+
+      context 'when multiple objects are being serialized' do
+        let(:resource) { create_list(:ci_pipeline, 2) }
+
+        it 'serializers the array of pipelines' do
+          expect(subject).not_to be_empty
+        end
+      end
+    end
+
+    context 'when used with pagination' do
+      let(:request) { spy('request') }
+      let(:response) { spy('response') }
+      let(:pagination) { {} }
+
+      before do
+        allow(request)
+          .to receive(:query_parameters)
+          .and_return(pagination)
+      end
+
+      let(:serializer) do
+        described_class.new(user: user)
+          .with_pagination(request, response)
+      end
+
+      it 'created a paginated serializer' do
+        expect(serializer).to be_paginated
+      end
+
+      context 'when resource does is not paginatable' do
+        context 'when a single pipeline object is being serialized' do
+          let(:resource) { create(:ci_empty_pipeline) }
+          let(:pagination) { { page: 1, per_page: 1 } }
+
+          it 'raises error' do
+            expect { subject }
+              .to raise_error(PipelineSerializer::InvalidResourceError)
+          end
+        end
+      end
+
+      context 'when resource is paginatable relation' do
+        let(:resource) { Ci::Pipeline.all }
+        let(:pagination) { { page: 1, per_page: 2 } }
+
+        context 'when a single pipeline object is present in relation' do
+          before { create(:ci_empty_pipeline) }
+
+          it 'serializes pipeline relation' do
+            expect(subject.first).to have_key :id
+          end
+        end
+
+        context 'when a multiple pipeline objects are being serialized' do
+          before { create_list(:ci_empty_pipeline, 3) }
+
+          it 'serializes appropriate number of objects' do
+            expect(subject.count).to be 2
+          end
+
+          it 'appends relevant headers' do
+            expect(response).to receive(:[]=).with('X-Total', '3')
+            expect(response).to receive(:[]=).with('X-Total-Pages', '2')
+            expect(response).to receive(:[]=).with('X-Per-Page', '2')
+
+            subject
+          end
+        end
+      end
     end
   end
 end