add test for merge request entity output

spec/ee/spec/serializers/merge_request_entity_spec.rb

@@ -4,13 +4,21 @@ describe MergeRequestEntity do
   let(:user) { create(:user) }
   let(:project) { create :project, :repository }
   let(:merge_request) { create(:merge_request, source_project: project, target_project: project) }
-  let(:build) { create(:ci_build, name: 'sast') }
+  let(:build) { create(:ci_build, name: 'job') }
   let(:request) { double('request', current_user: user) }
 
   subject do
     described_class.new(merge_request, request: request)
   end
 
+  it 'has performance data' do
+    allow(subject).to receive(:expose_performance_data?).and_return(true)
+    allow(merge_request).to receive(:base_performance_artifact).and_return(build)
+    allow(merge_request).to receive(:head_performance_artifact).and_return(build)
+
+    expect(subject.as_json).to include(:performance)
+  end
+
   it 'has sast data' do
     allow(subject).to receive(:expose_sast_data?).and_return(true)
     allow(merge_request).to receive(:sast_artifact).and_return(build)