What is the current state of the law on credible testimony?

agency previously determined that the applicant was not credible); Siewe v. Gonzales, 480 F.3d 160, 170 (2d Cir. 2007) ("[A] single false document or a single instance of false testimony may (if attributable to the petitioner) infect the balance of the alien's uncorroborated or unauthenticated evidence.").