Ask HN: Is there a "magic bullet" to test claims of Verizon/Comcast throttling?

There's been a lot of discussion about Verizon and Comcast throttling services like Netflix and Youtube. When someone claims that they found evidence, there are often comments saying that the method is flawed. If all these claims are not conclusive, what would be the "magic bullet" test? Could we do it by collectively sharing certain network results? Would testing the bit rate with VPN on/off help test these claims?