문제링크 : 통나무 건너뛰기
import sys
input=sys.stdin.readline
t=int(input())
for _ in range(t):
n=int(input())
list=[int(x) for x in input().split()]
list.sort(reverse=True)
result=0
for i in range(n-2):
result=max(result,list[i]-list[i+2])
print(result)