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: ''' D. MEX Sequences
  https://codeforces.com/contest/1613/problem/D
  '''
  
  import io, os, sys
  input = io.BytesIO(os.read(0,os.fstat(0).st_size)).readline  # decode().strip() if str
  output = sys.stdout.write
  
  DEBUG = os.environ.get('DEBUG') is not None
  
  if DEBUG:
      from varname.core import argname
      from inspect import currentframe
  
  def debug(var, *more_vars):
      if not DEBUG: return
      var_names = argname('var', '*more_vars', func=debug)
      values = (var, *more_vars)
      name_and_values = [f'{var_name}={value}'  for var_name, value in zip(var_names, values)]
      prefix = f'{currentframe().f_back.f_lineno:02d}: '
      print(f'{prefix}{", ".join(name_and_values)}')
  
  
  INF = float('inf')
  MOD = 998244353
  
  def solve(N, A):	
      # B[a] = num subsequences so far with val set {0,1,...,a}
      # C[a] = num subsequences so far with val set {0,1,...,a-2,a}
      B = [0]*(N+10)
      C = [0]*(N+10)
      B[-1] = 1
  
      # count num valid subsequences ending at each a:
      # * mex=a-1: {0,...,a-2}, {0,...,a-2,a}
      # * mex=a+1: {0,...,a-1}, {0,...,a}, {1,...,a,a+2}
      res = 0
      for a in A:
          add_b = B[a] + B[a-1]
          add_c = B[a-2] + C[a]
          add_c2 = C[a+2]
  
          B[a] = (B[a] + add_b) % MOD
          C[a] = (C[a] + add_c) % MOD
          C[a+2] = (C[a+2] + add_c2) % MOD
  
          res = (res + add_b + add_c + add_c2) % MOD
  
      return res
  
  
  def main():
      T = int(input())
      for _ in range(T):
          N = int(input())
          A = list(map(int, input().split()))
          out = solve(N, A)
          output(f'{out}\n')
  
  
  if __name__ == '__main__':
      main()
  
  