Testilying happen when a police officer give false testimony especially in criminal cases or trial when the Police lying persists despite audio or video evidence that has allowed the public to test the officers credibility.
This usually occurs in criminal trials that relies on the testimony of police officers but the police keep giving false testimony. This usually happen in a case where the police officer has been bribe to prevent him from saying the truth despite all available evidence of him testify falsely.
Testilying is telling lie under the oath by police officers. When the cops tend to cook up a lie in order to bring an innocent person to book, as seen in the question, falsifying an affidavit by the cops to get a criminal off the street is an act of Testilying by the cops