But could we trust their answer? If the robot says it is alive, how could we tell if it actually means it or is just saying it so we don't disassemble it?
Put a robot in a room. If you cannot tell the difference between him and a human by means of testing his mentality, without looking at them, then the robot is self-aware.
Why should self awareness count is the defining factor rather than consciousness? If we say that a squirrel is conscious but not self aware, does that make it okay to intentionally run them over?
A conscious computer rates no better than a squirrel if it isn't self aware. We may feel a little awkward about accidentally running it over with a car (like my dad did to his phone last month) but it's just a computer, not yet a person.
If the animal is not self-aware, his "rights" are given by humans, not requested by the animal.
These rights are ultimately about humans, not about animals - they are passive elements, not even accepting these rights or not.
And then, there are other problems:
In nature, predation (and all the pain it involves) is one of the main causes of death. The animals are part of the food chain - predators for some species, prey for other.
Can we even be certain a non-self-aware entity is sentient/can feel pain?
Some studies claim that animals can; other studies claim that the chemicals released are identical to the ones released during vigorous exercise.
What about a fly? Can it feel pain?
Ultimately, one can only be certain that someone is sentient is if he/she tells you this himself/herself AKA if it is self-aware/relatively intelligent.
And humans are not the ones above the minimal self-awareness/intelligence threshold needed for this; we are only the ones that are the furthest beyond this threshold.
At a substantial distance behind, you have bottlenose dolphins, chimpanzees, etc; all pressing against a "ceiling" represented by the intelligence needed to survive in their environments. It is still not known what caused our ancestors to leap-frog this obstacle so spectacularly and became far more intelligent than was actually needed for survival.