They're not deploying untested software, if that's what you're asking. They most likely simply deploy each change when it is ready, rather than building up work-in-progress and deploying many changes at the same time. It's a lot safer to change one thing at a time, see https://www.goodreads.com/en/book/show/35747076-accelerate. Releasing changes as soon as they are ready can also enable them to gather feedback faster - in this sense they would be iteratively 'testing' the product.