find assets in test for CI and local test

Due to the change in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/14583/diffs we
can't use the same method to access assets in a CI and the local test
environment anymore.

spec/models/project_services/jira_service_spec.rb

@@ -2,6 +2,7 @@ require 'spec_helper'
 
 describe JiraService do
   include Gitlab::Routing
+  include AssetsHelpers
 
   describe '#options' do
     let(:service) do
@@ -164,7 +165,7 @@ describe JiraService do
     it "creates Remote Link reference in JIRA for comment" do
       @jira_service.close_issue(merge_request, ExternalIssue.new("JIRA-123", project))
 
-      favicon_path = "http://localhost/assets/#{Rails.application.assets.find_asset('favicon.png').digest_path}"
+      favicon_path = "http://localhost/assets/#{find_asset('favicon.png').digest_path}"
 
       # Creates comment
       expect(WebMock).to have_requested(:post, @comment_url)

spec/services/system_note_service_spec.rb

@@ -3,6 +3,7 @@ require 'spec_helper'
 describe SystemNoteService do
   include Gitlab::Routing
   include RepoHelpers
+  include AssetsHelpers
 
   set(:group)    { create(:group) }
   set(:project)  { create(:project, :repository, group: group) }
@@ -769,7 +770,7 @@ describe SystemNoteService do
     end
 
     describe "new reference" do
-      let(:favicon_path) { "http://localhost/assets/#{Rails.application.assets.find_asset('favicon.png').digest_path}" }
+      let(:favicon_path) { "http://localhost/assets/#{find_asset('favicon.png').digest_path}" }
 
       before do
         allow(JIRA::Resource::Remotelink).to receive(:all).and_return([])

spec/support/helpers/assets_helpers.rb

@@ -0,0 +1,15 @@
+module AssetsHelpers
+  # In a CI environment the assets are not compiled, as there is a CI job
+  # `compile-assets` that compiles them in the prepare stage for all following
+  # specs.
+  # Locally the assets are precompiled dynamically.
+  #
+  # Sprockets doesn't provide one method to access an asset for both cases.
+  def find_asset(asset_name)
+    if ENV['CI']
+      Sprockets::Railtie.build_environment(Rails.application, true)[asset_name]
+    else
+      Rails.application.assets.find_asset(asset_name)
+    end
+  end
+end