Improve self-monitoring project specs

Previously the tests stubbed out the application settings and did not
test that the settings were properly invalidated to ensure that
PrometheusService had the latest settings to pass validations.  We now
use a real database object and `RequestStore` to emulate actual
behavior.

spec/lib/gitlab/database_importers/self_monitoring/project/create_service_spec.rb

@@ -50,7 +50,7 @@ describe Gitlab::DatabaseImporters::SelfMonitoring::Project::CreateService do
       end
     end
 
-    context 'with application settings and admin users' do
+    context 'with application settings and admin users', :request_store do
       let(:project) { result[:project] }
       let(:group) { result[:group] }
       let(:application_setting) { Gitlab::CurrentSettings.current_application_settings }
@@ -58,8 +58,9 @@ describe Gitlab::DatabaseImporters::SelfMonitoring::Project::CreateService do
       let!(:user) { create(:user, :admin) }
 
       before do
-        allow(ApplicationSetting).to receive(:current_without_cache) { application_setting }
-        application_setting.allow_local_requests_from_web_hooks_and_services = true
+        stub_env('IN_MEMORY_APPLICATION_SETTINGS', 'false')
+
+        application_setting.update(allow_local_requests_from_web_hooks_and_services: true)
       end
 
       shared_examples 'has prometheus service' do |listen_address|
@@ -130,12 +131,17 @@ describe Gitlab::DatabaseImporters::SelfMonitoring::Project::CreateService do
 
       it 'saves the project id' do
         expect(result[:status]).to eq(:success)
-        expect(application_setting.self_monitoring_project_id).to eq(project.id)
+        expect(application_setting.reload.self_monitoring_project_id).to eq(project.id)
       end
 
-      it 'expires application_setting cache' do
-        expect(Gitlab::CurrentSettings).to receive(:expire_current_application_settings)
+      it 'creates a Prometheus service' do
         expect(result[:status]).to eq(:success)
+
+        services = result[:project].reload.services
+
+        expect(services.count).to eq(1)
+        # Ensures PrometheusService#self_monitoring_project? is true
+        expect(services.first.allow_local_api_url?).to be_truthy
       end
 
       it 'creates an environment for the project' do
@@ -158,8 +164,8 @@ describe Gitlab::DatabaseImporters::SelfMonitoring::Project::CreateService do
       end
 
       it 'returns error when saving project ID fails' do
-        allow(application_setting).to receive(:update).and_call_original
-        allow(application_setting).to receive(:update)
+        allow(subject.application_settings).to receive(:update).and_call_original
+        allow(subject.application_settings).to receive(:update)
           .with(self_monitoring_project_id: anything)
           .and_return(false)
 
@@ -175,8 +181,8 @@ describe Gitlab::DatabaseImporters::SelfMonitoring::Project::CreateService do
         let(:existing_project) { create(:project, namespace: existing_group) }
 
         before do
-          application_setting.instance_administrators_group_id = existing_group.id
-          application_setting.self_monitoring_project_id = existing_project.id
+          application_setting.update(instance_administrators_group_id: existing_group.id,
+                                     self_monitoring_project_id: existing_project.id)
         end
 
         it 'returns success' do
@@ -189,7 +195,7 @@ describe Gitlab::DatabaseImporters::SelfMonitoring::Project::CreateService do
 
       context 'when local requests from hooks and services are not allowed' do
         before do
-          application_setting.allow_local_requests_from_web_hooks_and_services = false
+          application_setting.update(allow_local_requests_from_web_hooks_and_services: false)
         end
 
         it_behaves_like 'has prometheus service', 'http://localhost:9090'