Green’s Dictionary of Slang

(US police) of police, to offer perjured testimony in court.

1994		Mollen Report 36: [T]he practice of police falsification in connection with such arrests is so common in certain precincts that it has spawned its own word: ‘"testilying’.
1999		J. Maple Crime Fighter 226: When that cop goes to court, he won’t even be tempted to ‘testi-lie’.
2005		R. Cea No Lights, No Sirens 117: [T]he fewer cops who knew about our practices, the fewer people there would be to test-i-lie or, worse, tell the truth.
2009		D. Lehr Fence 70: The police perjury had a name: ‘testilying.’ The fabrications might be rooted in good intentions—to convict the guilty.
2020		L. Lungaro The 3-0 98: [T]hey would place the key on some drug dealer and come up with a fabricated story to tell the district attorney. This was called ‘test-i-lying’.