>What makes you think that? For large scale sites you need a parallel copy of the internet which doesn't exist. For example, we once caused a production incide

>What makes you think that? For large scale sites you need a parallel copy of the internet which doesn't exist. For example, we once caused a production incident (for us and other people) by simulating a major business event to our test stack and saturated links between <Cloud Provider> and <CDN Provider>. For future tests that was always an edge case that we couldn't fully test. Rinse and repeat those kinds of problems with every vender, service, and traffic source.