ISO 12207 has a rather non-standard (and very fuzzy!) distinction between verification and validation. In most circles, verification answers the question “did we build it right?” (does our product meet the requirements?), while validation means “was this the right thing to build” (do we have the right set of requirements?). ISO 12207 mentions requirements verification. How do you verify requirements, particularly the top level requirements? You don’t. You validate them.

The product on which I spend the bulk of my time used to distinguish verification from validation. Problems with this distinction popped up on an annoyingly frequent basis. The distinction was clear to me, but my interpretation wasn’t universally agreed upon. Is this a validation test or a verification test? Who cares? Why are we having this stupid fight? A rose by any other name smells just as sweet. The ultimate goal is to answer the question “Is it right?”

Our resolution to this ongoing imbroglio was to get rid of that distinction between verification and validation. We think of verification & validation as one word which together answer the question “Is it right?” We don’t split V&V into arbitrary parts. What we split into parts is how we go about answering that singular question. Whether you’re looking at our top level document or a detailed model document such as how we model gravity, chapter 5 is titled “Inspections, Tests, and Metrics”. The old title, “Verification and Validation”: It’s gone. We don’t split verification from validation. We instead split things into inspections, tests, and metrics. The chapter has typically has four sections, inspections, tests, traceability (typically automated), and metrics (also typically automated). Aside: Traceability analysis is just a specialized (but very important) kind of inspection. It’s elevated as a separate section because of it’s importance. We wrangled a tiny bit as to whether to call the chapter “Inspections, Tests, Traceability, and Metrics”. The answer was no. No more religious wars over names. Traceability is a kind of inspection; the title still fits.

Things that answer the question “is it right” without actually using the product goes under the heading of “inspections”. Requirements analysis, traceability analyses, analyses that demonstrate that the simplifying assumptions made by the model are acceptable for the model’s intended use: They’re all inspections because we didn’t use the product. Traceability, while an inspection, has a home of its own. Using the product to answer that question go under the rubric of “tests”. Everything from unit tests to tests against some artificial setup with a known analytic solution to integrated tests where we’re comparing the results from the product to real data collected from some previously flown vehicle: They’re all tests. Along the way we collect lots of metrics, many of them automated. Different levels of documents have different kinds of boring but important numbers. SLOC count, complexity, code coverage, number of waivers granted, number of issues in the CM system. Those boring but important numbers go under the rubric of “metrics”.

Our developers and testers love this change because now it’s crystal clear where things go. Project management loves this change because its consistent and because it removes all that silly wrangling over nomenclature. Our CMMI overlords love it because we’re still answering the right question (“Is it right”) and because we have a well defined process for getting there. Bean counters love it because we’re giving them lots of beans that they are very easy to find and very easy to count.

Validation ensures that the product actually meets the user’s needs, and that the specifications were correct in the first place, while verification is ensuring that the product has been built according to the requirements and design specifications.

what testing (unit, integration, system, uat) will be considered verification or validation?

Unit, Integration, and System testing are verification. UAT is validation.

So the question is, what testing (unit, integration, system, uat) will be considered verification or validation?

Generally, speaking on high level your example and explanation sounds good.

In your example: verification is about making sure that “there are two fields with max. length of 64 characters and Save button.” If some elements are missing according to requirement, then it does not pass verification. It is also a first step.

“validation is” – more about input and behavior of given required elements. In your case, it is validation of max. and min. input length, special character allowance, and any other related business rules.

All this is done on unit testing first and propagated to next stages if there are some related business-data flow.