There isn’t a one-size-fits-all answer. In the enterprise marketplace and eCommerce software development life cycle, the bare minimum is four:  Development environment – Developers should constantly test the code they write. Continuous Integration (CI) environment – the CI server will take care of testing the whole unit after each iteration push. QA environment – this is where end-to-end tests are run, manually, automatically, or both. Production environment – Testing in production (e.g., A/B testing) is essential for businesses that need to learn about their UX when using their software.