Add serializers tests

spec/serializers/cluster_entity_spec.rb

+require 'spec_helper'
+
+describe ClusterEntity do
+  set(:cluster) { create(:gcp_cluster, :errored) }
+  let(:request) { double('request') }
+
+  let(:entity) do
+    described_class.new(cluster)
+  end
+
+  describe '#as_json' do
+    subject { entity.as_json }
+
+    it 'contains status' do
+      expect(subject[:status]).to eq(:errored)
+    end
+
+    it 'contains status reason' do
+      expect(subject[:status_reason]).to eq('general error')
+    end
+  end
+end

spec/serializers/cluster_serializer_spec.rb

+require 'spec_helper'
+
+describe ClusterSerializer do
+  let(:serializer) do
+    described_class.new
+  end
+
+  describe '#represent_status' do
+    subject { serializer.represent_status(resource) }
+
+    context 'when represents only status' do
+      let(:resource) { create(:gcp_cluster, :errored) }
+
+      it 'serializes only status' do
+        expect(subject.keys).to contain_exactly(:status, :status_reason)
+      end
+    end
+  end
+end