The question is a little off target in that software development can be agile with either traditional QA phases or with more recent approaches like CI/CD. CI/C

The question is a little off target in that software development can be agile with either traditional QA phases or with more recent approaches like CI/CD. CI/CD seem to fit Agile better because you do not get a discontinuity of how a project is managed. But that by itself does not tell you if CI/CD is better or worse than QA phases of alpha and beta and a traditional test plan based on a functional spec. The CI/CD advantage is that you do not need a comprehensive test plan to start, and you start testing early. The disadvantage is that if what you have by the time you decide to ship does not cover both implementation and features you do not have test coverage, with the predictable problems. TDD and/or FDD can help you track whether you have test coverage. But if you do not have coverage, and you do not have regression testing, deploying will be painful, whether it is continuous or not.