Testing alone is not useful.
A test provides information, which is great, but doesn't actually accomplish anything by itself. The key is what you do about that information. Gathering data almost always implies some change:
- Changes in expectations. For example, "the tests say our limit is 1 TB/day". The action may be to adjust expectations; to say, "yes, the system as it stands is fast enough for us".
- Changes in software. A test finds a bug; the software change is to fix the bug.
- Changes in product planning or marketing. A test finds that a feature limit is too low for client needs. The marketing materials get changed, or the product plan for the next release gets "enhance this feature" added to it.
But all of those are actions that result from testing. Just testing only tells you the information; it doesn't do anything to deal with the information.
So don't accept requirements that something be tested. The requirement is that the feature works, or the speed is x, or the failure is handled gracefully. Be explicit about that; the test is a means to an end, but it's not an end in and of itself.