description: Let's call a sequence of integers x_1, x_2, ..., x_k MEX-correct if for all i (1 ≤ i ≤ k) |x_i - \operatorname{MEX}(x_1, x_2, ..., x_i)| ≤ 1 holds. Where \operatorname{MEX}(x_1, ..., x_k) is the minimum non-negative integer that doesn't belong to the set x_1, ..., x_k. For example, \operatorname{MEX}(1, 0, 1, 3) = 2 and \operatorname{MEX}(2, 1, 5) = 0.
  
  You are given an array a consisting of n non-negative integers. Calculate the number of non-empty MEX-correct subsequences of a given array. The number of subsequences can be very large, so print it modulo 998244353. 
  
  Note: a subsequence of an array a is a sequence [a_{i_1}, a_{i_2}, ..., a_{i_m}] meeting the constraints 1 ≤ i_1 < i_2 < ... < i_m ≤ n. If two different ways to choose the sequence of indices [i_1, i_2, ..., i_m] yield the same subsequence, the resulting subsequence should be counted twice (i. e. two subsequences are different if their sequences of indices [i_1, i_2, ..., i_m] are not the same).
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 10^5) — the number of test cases.
  
  The first line of each test case contains a single integer n (1 ≤ n ≤ 5 ⋅ 10^5).
  
  The second line contains n integers a_1, a_2, ..., a_n (0 ≤ a_i ≤ n).
  
  The sum of n over all test cases doesn't exceed 5 ⋅ 10^5.
  
  Output
  
  For each test case, print a single integer — the number of non-empty MEX-correct subsequences of a given array, taken modulo 998244353.
  
  Example
  
  Input
  
  
  4
  3
  0 2 1
  2
  1 0
  5
  0 0 0 0 0
  4
  0 1 2 3
  
  
  Output
  
  
  4
  2
  31
  7
  
  Note
  
  In the first example, the valid subsequences are [0], [1], [0,1] and [0,2].
  
  In the second example, the valid subsequences are [0] and [1].
  
  In the third example, any non-empty subsequence is valid. 
solution: import sys
  import math
  from collections import deque,Counter
  from sys import stdin
  
  #sys.setrecursionlimit(10**7)
  
  int1=lambda x: int(x)-1
  stinput=lambda :stdin.readline()[:-1]
  ii=lambda :int(stinput())
  mi=lambda :map(int, stdin.readline().split())
  li=lambda :list(mi())
  mi1=lambda :map(int1, stdin.readline().split())
  li1=lambda :list(mi1())
  mis=lambda :map(str, stdin.readline().split())
  
  pr=print
  rg=range
  
  from collections import defaultdict
  
  
  mod=10**9+7
  Mod=998244353
  INF=10**18
  ans=0
  
  def f(a):
    mex=0
    used=[0]*(n+2)
    for i in a:
      used[i]=1
      while used[mex]==1:
        mex+=1
      if abs(mex-i)>1:
        return False
    return True
  import random
  
  t=ii()
  
  for _ in range(t):
    n=ii()
    a=li()
    #n=8
    #a=[random.randint(0,5) for i in range(n)]
    dp0=[0]*(n+3)
    dp1=[0]*(n+3)
    dp2=[0]*(n+3)
    for i in a:
      if i==0:
        dp0[0]+=dp0[0]+1
        dp0[0]%=Mod
        dp2[1]+=dp2[1]+dp1[2]
        dp2[1]%=Mod
        
      else:
        dp0[i]+=dp0[i]+dp0[i-1]
        #dp0[i+1]+=dp1[i+1]
        dp0[i]%=Mod
        #dp0[i+1]%=Mod
        if i==1:
          dp1[1]*=2
          dp1[1]+=1
        else:
          dp1[i]*=2
          dp1[i]+=dp0[i-2]
        dp1[i]%=Mod
        dp2[i+1]+=dp2[i+1]+dp1[i+2]
        dp2[i-1]+=dp2[i-1]
        dp2[i+1]%=Mod
        dp2[i-1]%=Mod
      #print(dp0,dp1,dp2)
    #print(dp0,dp1)
    print((sum(dp0)+sum(dp1)+sum(dp2))%Mod)
    '''
    ans=0
    for bit in range(1,2**n):
      b=[]
      for i in range(n):
        if (bit>>i)&1:
          b.append(a[i])
      if f(b):
        ans+=1
        #print(b)
    print(ans)
    '''