Only mock ci connections in single db mode

Change `mock_ci_connection` to only setup a mocked
`Ci::ApplicationRecord` connection when running in a single database
mode. When running with multiple databases, we can use the actual
`Ci::ApplicationRecord` connection.

spec/support/database/multiple_databases.rb

@@ -6,6 +6,10 @@ module Database
       skip 'Skipping because multiple databases not set up' unless Gitlab::Database.has_config?(:ci)
     end
 
+    def skip_if_multiple_databases_are_setup
+      skip 'Skipping because multiple databases are set up' if Gitlab::Database.has_config?(:ci)
+    end
+
     def reconfigure_db_connection(name: nil, config_hash: {}, model: ActiveRecord::Base, config_model: nil)
       db_config = (config_model || model).connection_db_config
 
@@ -46,6 +50,25 @@ module Database
       new_handler&.clear_all_connections!
     end
     # rubocop:enable Database/MultipleDatabases
+
+    def with_mocked_ci_connection
+      if Gitlab::Database.has_config?(:ci)
+        yield
+      else
+        with_reestablished_active_record_base(reconnect: true) do
+          reconfigure_db_connection(
+            name: :ci,
+            model: Ci::ApplicationRecord,
+            config_model: ActiveRecord::Base
+          )
+
+          yield
+
+          # Cleanup connection_specification_name for Ci::ApplicationRecord
+          Ci::ApplicationRecord.remove_connection
+        end
+      end
+    end
   end
 
   module ActiveRecordBaseEstablishConnection
@@ -70,17 +93,8 @@ RSpec.configure do |config|
   end
 
   config.around(:each, :mocked_ci_connection) do |example|
-    with_reestablished_active_record_base(reconnect: true) do
-      reconfigure_db_connection(
-        name: :ci,
-        model: Ci::ApplicationRecord,
-        config_model: ActiveRecord::Base
-      )
-
+    with_mocked_ci_connection do
       example.run
-
-      # Cleanup connection_specification_name for Ci::ApplicationRecord
-      Ci::ApplicationRecord.remove_connection
     end
   end
 end

spec/support_specs/database/multiple_databases_spec.rb

@@ -56,4 +56,43 @@ RSpec.describe 'Database::MultipleDatabases' do
       end
     end
   end
+
+  describe '.with_mocked_ci_connection' do
+    context 'when only a single database is setup' do
+      before do
+        skip_if_multiple_databases_are_setup
+      end
+
+      it 'connects Ci::ApplicationRecord to the main database for the duration of the block', :aggregate_failures do
+        main_database = current_database(ActiveRecord::Base)
+        original_database = current_database(Ci::ApplicationRecord)
+
+        with_mocked_ci_connection do
+          expect(current_database(Ci::ApplicationRecord)).to eq(main_database)
+        end
+
+        expect(current_database(Ci::ApplicationRecord)).to eq(original_database)
+      end
+    end
+
+    context 'when multiple databases are setup' do
+      before do
+        skip_if_multiple_databases_not_setup
+      end
+
+      it 'does not mock the original Ci::ApplicationRecord connection', :aggregate_failures do
+        original_database = current_database(Ci::ApplicationRecord)
+
+        with_mocked_ci_connection do
+          expect(current_database(Ci::ApplicationRecord)).to eq(original_database)
+        end
+
+        expect(current_database(Ci::ApplicationRecord)).to eq(original_database)
+      end
+    end
+
+    def current_database(connection_class)
+      connection_class.retrieve_connection.execute('select current_database()').first
+    end
+  end
 end