Test migration helpers using a migration class

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -2,15 +2,13 @@ require 'spec_helper'
 
 describe Gitlab::Database::MigrationHelpers, lib: true do
   let(:model) do
-    Class.new do
-      include Gitlab::Database::MigrationHelpers
-
-      def method_missing(name, *args, &block)
-        ActiveRecord::Base.connection.send(name, *args, &block)
-      end
-    end.new
+    ActiveRecord::Migration.new.extend(
+      Gitlab::Database::MigrationHelpers
+    )
   end
 
+  before { allow(model).to receive(:puts) }
+
   describe '#add_concurrent_index' do
     context 'outside a transaction' do
       before do