A/B tests and feature flags are basically testing in prod. And yes, some of those features sometimes run as a "well, it should work, but we're not entirely sure

A/B tests and feature flags are basically testing in prod. And yes, some of those features sometimes run as a "well, it should work, but we're not entirely sure until we get a significant number of users using the system". It could be an edge case failing or scalability requirements being wrong. Another variation on the same theme is rewriting systems when you run production data through both systems. Quite often that's the only way of doin migrations to a new platform, or a new database, or yes, a newly re-written system. > Is it common practice to inject fabricated data into a prod system to run such tests? What's the best practice or prior art on doing this well? A very common practice is to run a snapshot of prod data (e.g. last hour, or last 24 hours, or even a week/month/year) through a system in staging (or cooking, or pre-cooking, or whatever name you give the system that's just about to be released). However, doing it properly may not be easy, and depends on the systems involved.