Initially, I would verify the output types of the function. It should exclusively return "heads" or "tails". Any other output would indicate a failure. def test_coin_flip ( flip ) : result = flip ( ) assert result in [ "heads" , "tails" ] , f"Unexpected output: { result } " Following that, I would assess the fairness of the function. Statistically, over a significant number of flips, the results should yield a roughly equal count of "heads" and "tails". def test_coin_flip_fairness ( flip , n = 100000 ) : results = [ flip ( ) for _ in range ( n ) ] heads = results . count ( "heads" ) tails = results . count ( "tails" ) # Asserting that the two counts are approximately equal assert abs ( heads - tails ) < n * 0.05 , f"Unfair distribution: { heads } heads vs { tails } tails" These evaluations will confirm that the function operates as intended for a coin flip.