Add spec for variables expressions with pipeline iid

spec/lib/gitlab/ci/pipeline/chain/populate_spec.rb

@@ -156,6 +156,7 @@ describe Gitlab::Ci::Pipeline::Chain::Populate do
     end
   end
 
+  context 'when variables policy is specified' do
     context 'when using only/except build policies' do
       let(:config) do
         { rspec: { script: 'rspec', stage: 'test', only: ['master'] },
@@ -173,5 +174,23 @@ describe Gitlab::Ci::Pipeline::Chain::Populate do
         expect(pipeline.stages.first.builds.size).to eq 1
         expect(pipeline.stages.first.builds.first.name).to eq 'rspec'
       end
+
+      context 'when variables expression is specified' do
+        let(:config) do
+          { rspec: { script: 'rspec', only: { variables: ["$CI_PIPELINE_IID == '1'"] } },
+            prod: { script: 'cap prod', only: { variables: ["$CI_PIPELINE_IID == '1000'"] } } }
+        end
+
+        context 'when pipeline iid is the subject' do
+          it 'populates pipeline according to used policies' do
+            step.perform!
+
+            expect(pipeline.stages.size).to eq 1
+            expect(pipeline.stages.first.builds.size).to eq 1
+            expect(pipeline.stages.first.builds.first.name).to eq 'rspec'
+          end 
+        end
+      end
+    end
   end
 end