Some may recall that the POET design provides the ability for end to end testing while in wafer form using loopback waveguides which connect the transmit  waveguides to the receive waveguides. The loopback is at the edge of each engine boundary and is removed when the wafer is sliced and diced.

From the tweet: The transition towards semiconductorization processes is achieved through wafer-scale assembly and testing where all photonic components, such as lasers and photo diodes , are passively attached at wafer scale and tested  before singulation.