Acceptance criteria are a range of conditions that a given product must satisfy before the end-user, consumer, or group of stakeholders accepts it.
Fixed price contracts can be rather tricky in a Scrum environment. Classic software development and Agile software development are very different from one another, and things that work in one environment don’t necessarily work in another.
The simple answer is, yes. Agile teams still need to adhere to the basics of testing, however, their approach allows them to go about it quite differently.