The best approach I’ve seen is to do all of the above. - Have QA run pessimal versions of real use cases. Trying to sell a word processor to lawyers? Format

The best approach I’ve seen is to do all of the above. - Have QA run pessimal versions of real use cases. Trying to sell a word processor to lawyers? Format the entire US legal code and a bajillion contracts in it, then duplicate it 10x and start filing usability/performance bugs. - Have the engineers test everything with randomly generated workloads before committing. Run those tests nightly, and fix all the crashes / failures. - Have Product Management (remember them?) work with marketing and sales to figure out what absolutely has to ship, and when. Make sure it only takes one of the above three groups to stop ship, and also to stop non-essential development tasks.