C=0
for t in range(int(input())):
  N=int(input())
  C+=N*N
  if C>=10000000:
    assert(0)
  A=[0]+sorted(map(int,input().split()))
  B=[]
  for i in range(N,0,-1):
    B.append(A[i]-A[i-1])
  B=B[::-1]
  K=(N+1)//2
  DP=[[0]*(K+1) for i in range(N+1)]
  for i in range(N):
    for j in range(K+1):
      DP[i+1][j]=max(DP[i+1][j],DP[i][j])
      if j<K:
        DP[i+1][j+1]=max(DP[i+1][j+1],DP[i][j]+B[i])
  print(DP[N][K])