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 java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.PrintWriter;
  import java.util.*;
  
  
  public class Main {
      static int i, j, k, n, m, t, y, x, sum = 0;
      static long mod =  998244353;
      static FastScanner fs = new FastScanner();
      static PrintWriter out = new PrintWriter(System.out);
      static String str;
      static long ans;
  
  
  
      public static void main(String[] args) {
  
          t = fs.nextInt();
  
          while(t-- >0) {
  
              n = fs.nextInt();
              int[] arr = fs.readArray(n);
              long[][] dp = new long[n+5][2];
  
              for(i=0;i<n;i++){
  
                  //x-1 is mex
                  if(arr[i]-1>=0){
                      dp[arr[i]-1][1]*= 2;
                      dp[arr[i]-1][1]%=mod;
                      dp[arr[i]-1][1]+= dp[arr[i]-1][0];
                      dp[arr[i]-1][1]%=mod;
                  }
  
                  //x is mex
  
                  dp[arr[i]+1][0]*=2;
                  dp[arr[i]+1][0]%=mod;
  
  
                  dp[arr[i]+1][0]+=dp[arr[i]][0];
                  dp[arr[i]+1][0]%=mod;
  
  
                  dp[arr[i]+1][1]*=2;
                  dp[arr[i]+1][1]%=mod;
  
                  if(arr[i]==0) {
                      dp[1][0]++;
                      dp[1][0] %= mod;
                  }
                  if(arr[i]==1) {
                      dp[0][1]++;
                      dp[0][1]%=mod;
                  }
  
              }
  
              ans=0;
              for(i=0;i<=n+2;i++){
                  ans+=dp[i][0];
                  ans%=mod;
                  ans+=dp[i][1];
                  ans%=mod;
              }
  
              out.println(ans);
  
          }
          out.close();
      }
  
      static long find(long l, long r, long n, long k, long target){
          long m = (l+r)/2;
  
          long temp = m*(k-1);
  
          if(target - temp>0 && target - temp<n)
              return m;
  
          else if(temp>=target)
              return find(l,m-1,n,k,target);
          else
              return find(m+1,r,n,k,target);
      }
  
  
     /*static long nck(int n , int k){
          long a = fact[n];
          long b = modInv(fact[k]);
          b*= modInv(fact[n-k]);
          b%=mod;
  
          return (a*b)%mod;
      }
  
     static void populateFact(){
          fact[0]=1;
  
          fact[1] = 1;
  
          for(i=2;i<300005;i++){
              fact[i]=i*fact[i-1];
              fact[i]%=mod;
          }
      }
      */
  
  
      static long gcd(long a, long b)
      {
          if (b == 0)
              return a;
          return gcd(b, a % b);
      }
  
      static long exp(long base, long pow) {
          if (pow==0) return 1;
          long half=exp(base, pow/2);
          if (pow%2==0) return mul(half, half);
          return mul(half, mul(half, base));
      }
  
      static long mul(long a, long b) {
          return ((a%mod)*(b%mod))%mod;
      }
  
      static long add(long a, long b) {
          return ((a%mod)+(b%mod))%mod;
      }
  
      static long modInv(long x) {
          return exp(x, mod-2);
      }
  
      static void ruffleSort(int[] a) {
          //ruffle
          int n = a.length;
          Random r = new Random();
          for (int i = 0; i < a.length; i++) {
              int oi = r.nextInt(n), temp = a[i];
              a[i] = a[oi];
              a[oi] = temp;
          }
  
          //then sort
          Arrays.sort(a);
      }
  
      static void ruffleSort(long[] a) {
          //ruffle
          int n = a.length;
          Random r = new Random();
          for (int i = 0; i < a.length; i++) {
              int oi = r.nextInt(n);
              long temp = a[i];
              a[i] = a[oi];
              a[oi] = temp;
          }
  
          Arrays.sort(a);
      }
  
      static class FastScanner {
          BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
          StringTokenizer st = new StringTokenizer("");
  
          String next() {
              while (!st.hasMoreTokens())
                  try {
                      st = new StringTokenizer(br.readLine());
                  } catch (IOException e) {
                      e.printStackTrace();
                  }
              return st.nextToken();
          }
  
          int nextInt() {
              return Integer.parseInt(next());
          }
  
          int[] readArray(int n) {
              int[] a=new int[n];
              for (int i=0; i<n; i++) a[i]=nextInt();
              return a;
          }
  
          long nextLong() {
              return Long.parseLong(next());
          }
      }
  
      static class Pair implements Comparable<Pair>{
          public int x, y;
  
          Pair(int x, int y){
              this.x = x;
              this.y = y;
          }
  
          @Override
          public int compareTo(Pair o) {
  
              if(x==o.x)
                  return Integer.compare(y,o.y);
  
              return Integer.compare(x,o.x);
          }
  
  
      }
  
  
  }