Test if expanded_environment_name could expand var

with symbols. Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/8088#note_20234245

spec/models/build_spec.rb

@@ -1306,11 +1306,25 @@ describe Ci::Build, models: true do
   describe '#expanded_environment_name' do
     subject { build.expanded_environment_name }
 
-    context 'when environment uses variables' do
-      let(:build) { create(:ci_build, ref: 'master', environment: 'review/$CI_BUILD_REF_NAME') }
+    context 'when environment uses $CI_BUILD_REF_NAME' do
+      let(:build) do
+        create(:ci_build,
+               ref: 'master',
+               environment: 'review/$CI_BUILD_REF_NAME')
+      end
 
       it { is_expected.to eq('review/master') }
     end
+
+    context 'when environment uses yaml_variables containing symbol keys' do
+      let(:build) do
+        create(:ci_build,
+               yaml_variables: [{key: :APP_HOST, value: 'host'}],
+               environment: 'review/$APP_HOST')
+      end
+
+      it { is_expected.to eq('review/host') }
+    end
   end
 
   describe '#detailed_status' do