write a go solution for 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-operatornameMEX(x_1,x_2,...,x_i)|<=1 holds. Where operatornameMEX(x_1,...,x_k) is the minimum non-negative integer that doesn't belong to the set x_1,...,x_k. For example, operatornameMEX(1,0,1,3)=2 and operatornameMEX(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 Format:
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 Format:
For each test case, print a single integer — the number of non-empty MEX-correct subsequences of a given array, taken modulo 998244353.

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.. Output only the code with no comments, explanation, or additional text.