Until you have found product-market fit, your production environment is often just another test environment. It’s not testing your code, it’s testing your customers.
At a previous startup company, we had a few hundred thousand users. Not all that many, but enough to get some interesting data and be in a position to use it to optimize the business. We had previously built a recommendation engine in Elasticsearch which all our users were piped through, and we user it to provide daily recommendations based on our most recent data.