#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>
#include <atcoder/modint>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

using mint = atcoder::modint998244353;

ostream& operator<<(ostream& os, const mint& m){
    os << m.val();
    return os;
}

#define N_MAX 200002
mint inv[N_MAX],fac[N_MAX],finv[N_MAX];

void init(){
    const ll MOD = mint::mod();
    fac[0]=1;fac[1]=1;
    finv[0]=1;finv[1]=1;
    inv[1]=1;
    for(int i=2;i<N_MAX;i++){
        inv[i]=mint(MOD)-inv[MOD%i]*(MOD/i);
        fac[i]=fac[i-1]*(ll) i;
        finv[i]=finv[i-1]*inv[i];
    }
}

mint comb(ll n, ll r){
    if(n < r){
        return mint(0);
    }else{
        return fac[n]*finv[r]*finv[n-r];
    }
}

#define endl "\n"

void solve(){
    int n, m; cin >> n >> m;
    vector<int> cnt(n);
    for(int i = 0; i < n; i++){
        int x; cin >> x;
        cnt[x]++;
    }
    mint ans = 1;
    int blocks = 0;
    int l = 0, r = 0;
    for(int x = n-1; x >= 0; x--){
        if(cnt[x] == 0) continue;
        if(l > x || r > x){
            cout << 0 << endl;
            return;
        }
        if(l == x){
            if(n-(l+cnt[x]) > x){
                cout << 0 << endl;
                return;
            }
            blocks++;
            continue;
        }
        if(r == x){
            if(n-(r+cnt[x]) > x){
                cout << 0 << endl;
                return;
            }
            blocks++;
            continue;
        }
        if(l+cnt[x] == n-x && r+cnt[x] == n-x){
            ans *= 2;
            l += cnt[x];
            blocks++;
            continue;
        }
        if(l+cnt[x] == n-x){
            l += cnt[x];
            blocks++;
            continue;
        }
        if(r+cnt[x] == n-x){
            r += cnt[x];
            blocks++;
            continue;
        }
        if(l+r+cnt[x] == 2*(n-x)){
            int lx = n-x-l;
            int rx = n-x-r;
            if(lx < 0 || rx < 0){
                cout << 0 << endl;
                return;
            }
            ans *= comb(cnt[x], lx);
            blocks += 2;
            l = n-x;
            r = n-x;
            continue;
        }
        cout << 0 << endl;
        return;
    }
    ans *= comb(m, blocks);
    cout << ans << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    init();
    int t; cin >> t;
    while(t--) solve();
}