10 August 2018
Testilying is a blend of testify and lying and refers to someone, especially a police officer, committing perjury. It seems to have first arisen within the ranks of the New York City police department in the early 1990s. The term came into the public consciousness as a result of a 1994 investigation into corruption in that department.
The earliest citation I have found is from a 22 April 1994 New York Times article:
New York City police officers often make false arrests, tamper with evidence and commit perjury on the witness stand [...] And it is prevalent enough in the department that it has its own nickname: “testilying.”
Source:
Sexton, Joe. “‘New York Police Often Lie Under Oath, Report Says.” New York Times, 22 April 1994, A1.