There are some major problems with TestAdversary (based on A Killer Adversary for Quicksort by M. D. McIlroy).

1. The data field is modified by Swap() but ignored by Less(), so swapping has no effect.

2. Less() compares elements using >=, which is messed up.

3. The test never checks anything, so it will always pass. It should count the number of comparisons and fail if there are too many.

4. The size 100 is too small to distinguish between O(n^2) with a small constant factor and O(n*log(n)).

5. (nitpicking) map[int]int can be replaced with []int, which is much more efficient.