"Test to Destruction" is a novelette by Keith Laumer from Harlan Ellison's science fiction anthology Dangerous Visions (1967). It also appears in A Plague of Demons and Other Stories, a posthumous Laumer omnibus edited by Eric Flint and published in 2003.
Plot
The leader of a rebellion is questioned in mental torture device chair. An alien mind probe finds him as the most powerful mental emission from the planet at the time. The aliens try to test him to destruction.
References
Test to Destruction Wikipedia(Text) CC BY-SA